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Chapter 7 of 14
NCERT Solutions

Binomial Theorem

Rajasthan Board · Class 11 · Mathematics

NCERT Solutions for Binomial Theorem — Rajasthan Board Class 11 Mathematics.

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Exercise 7.1

1Expand (12x)5(1-2x)^5.Show solution
Given: (12x)5(1-2x)^5

Formula (Binomial Theorem):
(a+b)n=r=0nnCranrbr(a+b)^n = \sum_{r=0}^{n} {}^nC_r\, a^{n-r}\, b^r

Here a=1a=1, b=2xb=-2x, n=5n=5.

(12x)5=5C0(1)5+5C1(1)4(2x)+5C2(1)3(2x)2+5C3(1)2(2x)3+5C4(1)(2x)4+5C5(2x)5
(1-2x)^5 = {}^5C_0(1)^5 + {}^5C_1(1)^4(-2x) + {}^5C_2(1)^3(-2x)^2 + {}^5C_3(1)^2(-2x)^3 + {}^5C_4(1)(-2x)^4 + {}^5C_5(-2x)^5


=1+5(2x)+10(4x2)+10(8x3)+5(16x4)+1(32x5)= 1 + 5(-2x) + 10(4x^2) + 10(-8x^3) + 5(16x^4) + 1(-32x^5)

=110x+40x280x3+80x432x5\boxed{= 1 - 10x + 40x^2 - 80x^3 + 80x^4 - 32x^5}
2Expand (2xx2)5\left(\dfrac{2}{x}-\dfrac{x}{2}\right)^5.Show solution
Given: (2xx2)5\left(\dfrac{2}{x}-\dfrac{x}{2}\right)^5

Here a=2xa=\dfrac{2}{x}, b=x2b=-\dfrac{x}{2}, n=5n=5.

(2xx2)5=r=055Cr(2x)5r(x2)r\left(\frac{2}{x}-\frac{x}{2}\right)^5 = \sum_{r=0}^{5}{}^5C_r\left(\frac{2}{x}\right)^{5-r}\left(-\frac{x}{2}\right)^r

Computing each term:

- r=0r=0: 5C0(2x)5=32x5{}^5C_0\left(\dfrac{2}{x}\right)^5 = \dfrac{32}{x^5}

- r=1r=1: 5C1(2x)4(x2)=516x4(x2)=40x3{}^5C_1\left(\dfrac{2}{x}\right)^4\left(-\dfrac{x}{2}\right) = 5\cdot\dfrac{16}{x^4}\cdot\left(-\dfrac{x}{2}\right) = -\dfrac{40}{x^3}

- r=2r=2: 5C2(2x)3(x2)2=108x3x24=20x{}^5C_2\left(\dfrac{2}{x}\right)^3\left(-\dfrac{x}{2}\right)^2 = 10\cdot\dfrac{8}{x^3}\cdot\dfrac{x^2}{4} = \dfrac{20}{x}

- r=3r=3: 5C3(2x)2(x2)3=104x2(x38)=5x{}^5C_3\left(\dfrac{2}{x}\right)^2\left(-\dfrac{x}{2}\right)^3 = 10\cdot\dfrac{4}{x^2}\cdot\left(-\dfrac{x^3}{8}\right) = -5x

- r=4r=4: 5C4(2x)(x2)4=52xx416=5x38{}^5C_4\left(\dfrac{2}{x}\right)\left(-\dfrac{x}{2}\right)^4 = 5\cdot\dfrac{2}{x}\cdot\dfrac{x^4}{16} = \dfrac{5x^3}{8}

- r=5r=5: 5C5(x2)5=x532{}^5C_5\left(-\dfrac{x}{2}\right)^5 = -\dfrac{x^5}{32}

(2xx2)5=32x540x3+20x5x+5x38x532\boxed{\left(\frac{2}{x}-\frac{x}{2}\right)^5 = \frac{32}{x^5} - \frac{40}{x^3} + \frac{20}{x} - 5x + \frac{5x^3}{8} - \frac{x^5}{32}}
3Expand (2x3)6(2x-3)^6.Show solution
Given: (2x3)6(2x-3)^6

Here a=2xa=2x, b=3b=-3, n=6n=6.

(2x3)6=r=066Cr(2x)6r(3)r(2x-3)^6 = \sum_{r=0}^{6}{}^6C_r(2x)^{6-r}(-3)^r

Computing each term:

- r=0r=0: 6C0(2x)6=64x6{}^6C_0(2x)^6 = 64x^6
- r=1r=1: 6C1(2x)5(3)=632x5(3)=576x5{}^6C_1(2x)^5(-3) = 6\cdot32x^5\cdot(-3) = -576x^5
- r=2r=2: 6C2(2x)4(9)=1516x49=2160x4{}^6C_2(2x)^4(9) = 15\cdot16x^4\cdot9 = 2160x^4
- r=3r=3: 6C3(2x)3(27)=208x3(27)=4320x3{}^6C_3(2x)^3(-27) = 20\cdot8x^3\cdot(-27) = -4320x^3
- r=4r=4: 6C4(2x)2(81)=154x281=4860x2{}^6C_4(2x)^2(81) = 15\cdot4x^2\cdot81 = 4860x^2
- r=5r=5: 6C5(2x)(243)=62x(243)=2916x{}^6C_5(2x)(-243) = 6\cdot2x\cdot(-243) = -2916x
- r=6r=6: 6C6(3)6=729{}^6C_6(-3)^6 = 729

(2x3)6=64x6576x5+2160x44320x3+4860x22916x+729\boxed{(2x-3)^6 = 64x^6 - 576x^5 + 2160x^4 - 4320x^3 + 4860x^2 - 2916x + 729}
4Expand (x3+1x)5\left(\dfrac{x}{3}+\dfrac{1}{x}\right)^5.Show solution
Given: (x3+1x)5\left(\dfrac{x}{3}+\dfrac{1}{x}\right)^5

Here a=x3a=\dfrac{x}{3}, b=1xb=\dfrac{1}{x}, n=5n=5.

(x3+1x)5=r=055Cr(x3)5r(1x)r\left(\frac{x}{3}+\frac{1}{x}\right)^5 = \sum_{r=0}^{5}{}^5C_r\left(\frac{x}{3}\right)^{5-r}\left(\frac{1}{x}\right)^r

Computing each term:

- r=0r=0: 5C0(x3)5=x5243{}^5C_0\left(\dfrac{x}{3}\right)^5 = \dfrac{x^5}{243}

- r=1r=1: 5C1(x3)4(1x)=5x4811x=5x381{}^5C_1\left(\dfrac{x}{3}\right)^4\left(\dfrac{1}{x}\right) = 5\cdot\dfrac{x^4}{81}\cdot\dfrac{1}{x} = \dfrac{5x^3}{81}

- r=2r=2: 5C2(x3)3(1x)2=10x3271x2=10x27{}^5C_2\left(\dfrac{x}{3}\right)^3\left(\dfrac{1}{x}\right)^2 = 10\cdot\dfrac{x^3}{27}\cdot\dfrac{1}{x^2} = \dfrac{10x}{27}

- r=3r=3: 5C3(x3)2(1x)3=10x291x3=109x{}^5C_3\left(\dfrac{x}{3}\right)^2\left(\dfrac{1}{x}\right)^3 = 10\cdot\dfrac{x^2}{9}\cdot\dfrac{1}{x^3} = \dfrac{10}{9x}

- r=4r=4: 5C4(x3)(1x)4=5x31x4=53x3{}^5C_4\left(\dfrac{x}{3}\right)\left(\dfrac{1}{x}\right)^4 = 5\cdot\dfrac{x}{3}\cdot\dfrac{1}{x^4} = \dfrac{5}{3x^3}

- r=5r=5: 5C5(1x)5=1x5{}^5C_5\left(\dfrac{1}{x}\right)^5 = \dfrac{1}{x^5}

(x3+1x)5=x5243+5x381+10x27+109x+53x3+1x5\boxed{\left(\frac{x}{3}+\frac{1}{x}\right)^5 = \frac{x^5}{243}+\frac{5x^3}{81}+\frac{10x}{27}+\frac{10}{9x}+\frac{5}{3x^3}+\frac{1}{x^5}}
5Expand (x+1x)6\left(x+\dfrac{1}{x}\right)^6.Show solution
Given: (x+1x)6\left(x+\dfrac{1}{x}\right)^6

Here a=xa=x, b=1xb=\dfrac{1}{x}, n=6n=6.

(x+1x)6=r=066Crx6r(1x)r=r=066Crx62r\left(x+\frac{1}{x}\right)^6 = \sum_{r=0}^{6}{}^6C_r\, x^{6-r}\left(\frac{1}{x}\right)^r = \sum_{r=0}^{6}{}^6C_r\, x^{6-2r}

Computing each term:

- r=0r=0: 6C0x6=x6{}^6C_0\, x^6 = x^6
- r=1r=1: 6C1x4=6x4{}^6C_1\, x^4 = 6x^4
- r=2r=2: 6C2x2=15x2{}^6C_2\, x^2 = 15x^2
- r=3r=3: 6C3x0=20{}^6C_3\, x^0 = 20
- r=4r=4: 6C4x2=15x2{}^6C_4\, x^{-2} = \dfrac{15}{x^2}
- r=5r=5: 6C5x4=6x4{}^6C_5\, x^{-4} = \dfrac{6}{x^4}
- r=6r=6: 6C6x6=1x6{}^6C_6\, x^{-6} = \dfrac{1}{x^6}

(x+1x)6=x6+6x4+15x2+20+15x2+6x4+1x6\boxed{\left(x+\frac{1}{x}\right)^6 = x^6 + 6x^4 + 15x^2 + 20 + \frac{15}{x^2} + \frac{6}{x^4} + \frac{1}{x^6}}
6Using binomial theorem, evaluate (96)3(96)^3.Show solution
Write: 96=100496 = 100 - 4

(96)3=(1004)3(96)^3 = (100-4)^3

=3C0(100)33C1(100)2(4)+3C2(100)(4)23C3(4)3= {}^3C_0(100)^3 - {}^3C_1(100)^2(4) + {}^3C_2(100)(4)^2 - {}^3C_3(4)^3

=10000003×10000×4+3×100×1664= 1000000 - 3\times10000\times4 + 3\times100\times16 - 64

=1000000120000+480064= 1000000 - 120000 + 4800 - 64

(96)3=884736\boxed{(96)^3 = 884736}
7Using binomial theorem, evaluate (102)5(102)^5.Show solution
Write: 102=100+2102 = 100 + 2

(102)5=(100+2)5(102)^5 = (100+2)^5

=5C0(100)5+5C1(100)4(2)+5C2(100)3(2)2+5C3(100)2(2)3+5C4(100)(2)4+5C5(2)5= {}^5C_0(100)^5 + {}^5C_1(100)^4(2) + {}^5C_2(100)^3(2)^2 + {}^5C_3(100)^2(2)^3 + {}^5C_4(100)(2)^4 + {}^5C_5(2)^5

=10000000000+5×100000000×2+10×1000000×4+10×10000×8+5×100×16+32= 10000000000 + 5\times100000000\times2 + 10\times1000000\times4 + 10\times10000\times8 + 5\times100\times16 + 32

=10000000000+1000000000+40000000+800000+8000+32= 10000000000 + 1000000000 + 40000000 + 800000 + 8000 + 32

(102)5=11040808032\boxed{(102)^5 = 11040808032}
8Using binomial theorem, evaluate (101)4(101)^4.Show solution
Write: 101=100+1101 = 100 + 1

(101)4=(100+1)4(101)^4 = (100+1)^4

=4C0(100)4+4C1(100)3(1)+4C2(100)2(1)2+4C3(100)(1)3+4C4(1)4= {}^4C_0(100)^4 + {}^4C_1(100)^3(1) + {}^4C_2(100)^2(1)^2 + {}^4C_3(100)(1)^3 + {}^4C_4(1)^4

=100000000+4×1000000+6×10000+4×100+1= 100000000 + 4\times1000000 + 6\times10000 + 4\times100 + 1

=100000000+4000000+60000+400+1= 100000000 + 4000000 + 60000 + 400 + 1

(101)4=104060401\boxed{(101)^4 = 104060401}
9Using binomial theorem, evaluate (99)5(99)^5.Show solution
Write: 99=100199 = 100 - 1

(99)5=(1001)5(99)^5 = (100-1)^5

=5C0(100)55C1(100)4+5C2(100)35C3(100)2+5C4(100)5C5= {}^5C_0(100)^5 - {}^5C_1(100)^4 + {}^5C_2(100)^3 - {}^5C_3(100)^2 + {}^5C_4(100) - {}^5C_5

=100000000005×100000000+10×100000010×10000+5×1001= 10000000000 - 5\times100000000 + 10\times1000000 - 10\times10000 + 5\times100 - 1

=10000000000500000000+10000000100000+5001= 10000000000 - 500000000 + 10000000 - 100000 + 500 - 1

(99)5=9509900499\boxed{(99)^5 = 9509900499}
10Using Binomial Theorem, indicate which number is larger (1.1)10000(1.1)^{10000} or 10001000.Show solution
We show that (1.1)^{10000} > 1000.

Write 1.1=1+0.11.1 = 1 + 0.1. By the Binomial Theorem:

(1.1)10000=(1+0.1)10000(1.1)^{10000} = (1+0.1)^{10000}

=10000C0+10000C1(0.1)+10000C2(0.1)2+= {}^{10000}C_0 + {}^{10000}C_1(0.1) + {}^{10000}C_2(0.1)^2 + \cdots

All terms are positive. Taking only the first two terms:

(1.1)^{10000} > {}^{10000}C_0 + {}^{10000}C_1(0.1)

=1+10000×0.1= 1 + 10000 \times 0.1

= 1 + 1000 = 1001 > 1000

\therefore\quad \boxed{(1.1)^{10000} > 1000}
11Find (a+b)4(ab)4(a+b)^4-(a-b)^4. Hence, evaluate (3+2)4(32)4(\sqrt{3}+\sqrt{2})^4-(\sqrt{3}-\sqrt{2})^4.Show solution
Step 1: Expand (a+b)4(a+b)^4 and (ab)4(a-b)^4.

(a+b)4=4C0a4+4C1a3b+4C2a2b2+4C3ab3+4C4b4(a+b)^4 = {}^4C_0 a^4 + {}^4C_1 a^3b + {}^4C_2 a^2b^2 + {}^4C_3 ab^3 + {}^4C_4 b^4
=a4+4a3b+6a2b2+4ab3+b4= a^4 + 4a^3b + 6a^2b^2 + 4ab^3 + b^4

(ab)4=a44a3b+6a2b24ab3+b4(a-b)^4 = a^4 - 4a^3b + 6a^2b^2 - 4ab^3 + b^4

Step 2: Subtract.

(a+b)4(ab)4=2(4a3b+4ab3)=8a3b+8ab3=8ab(a2+b2)(a+b)^4-(a-b)^4 = 2(4a^3b + 4ab^3) = 8a^3b + 8ab^3 = 8ab(a^2+b^2)

Step 3: Substitute a=3a=\sqrt{3}, b=2b=\sqrt{2}.

(3+2)4(32)4=8(3)(2)[(3)2+(2)2](\sqrt{3}+\sqrt{2})^4-(\sqrt{3}-\sqrt{2})^4 = 8(\sqrt{3})(\sqrt{2})\left[(\sqrt{3})^2+(\sqrt{2})^2\right]

=86(3+2)=86×5= 8\sqrt{6}\,(3+2) = 8\sqrt{6}\times 5

=406\boxed{= 40\sqrt{6}}
12Find (x+1)6+(x1)6(x+1)^6+(x-1)^6. Hence or otherwise evaluate (2+1)6+(21)6(\sqrt{2}+1)^6+(\sqrt{2}-1)^6.Show solution
Step 1: Expand (x+1)6(x+1)^6 and (x1)6(x-1)^6.

(x+1)6=6C0x6+6C1x5+6C2x4+6C3x3+6C4x2+6C5x+6C6(x+1)^6 = {}^6C_0 x^6 + {}^6C_1 x^5 + {}^6C_2 x^4 + {}^6C_3 x^3 + {}^6C_4 x^2 + {}^6C_5 x + {}^6C_6

(x1)6=6C0x66C1x5+6C2x46C3x3+6C4x26C5x+6C6(x-1)^6 = {}^6C_0 x^6 - {}^6C_1 x^5 + {}^6C_2 x^4 - {}^6C_3 x^3 + {}^6C_4 x^2 - {}^6C_5 x + {}^6C_6

Step 2: Add (odd-power terms cancel).

(x+1)6+(x1)6=2[6C0x6+6C2x4+6C4x2+6C6](x+1)^6+(x-1)^6 = 2\left[{}^6C_0 x^6 + {}^6C_2 x^4 + {}^6C_4 x^2 + {}^6C_6\right]

=2[x6+15x4+15x2+1]= 2\left[x^6 + 15x^4 + 15x^2 + 1\right]

Step 3: Substitute x=2x=\sqrt{2}.

(2+1)6+(21)6=2[(2)6+15(2)4+15(2)2+1](\sqrt{2}+1)^6+(\sqrt{2}-1)^6 = 2\left[(\sqrt{2})^6 + 15(\sqrt{2})^4 + 15(\sqrt{2})^2 + 1\right]

=2[8+15×4+15×2+1]= 2\left[8 + 15\times4 + 15\times2 + 1\right]

=2[8+60+30+1]=2×99= 2\left[8 + 60 + 30 + 1\right] = 2\times99

=198\boxed{= 198}
13Show that 9n+18n99^{n+1}-8n-9 is divisible by 64, whenever nn is a positive integer.Show solution
We need to show: 9n+18n9=64k9^{n+1}-8n-9 = 64k for some non-negative integer kk.

Write 9=1+89 = 1+8, so 9n+1=(1+8)n+19^{n+1} = (1+8)^{n+1}.

By the Binomial Theorem:

(1+8)n+1=n+1C0+n+1C1(8)+n+1C2(8)2+n+1C3(8)3++n+1Cn+1(8)n+1(1+8)^{n+1} = {}^{n+1}C_0 + {}^{n+1}C_1(8) + {}^{n+1}C_2(8)^2 + {}^{n+1}C_3(8)^3 + \cdots + {}^{n+1}C_{n+1}(8)^{n+1}

=1+(n+1)8+n+1C264+n+1C383+= 1 + (n+1)\cdot8 + {}^{n+1}C_2\cdot64 + {}^{n+1}C_3\cdot8^3 + \cdots

=1+8n+8+64[n+1C2+n+1C38++8n1]= 1 + 8n + 8 + 64\left[{}^{n+1}C_2 + {}^{n+1}C_3\cdot8 + \cdots + 8^{n-1}\right]

Therefore:

9n+18n9=1+8n+8+64M8n99^{n+1} - 8n - 9 = 1 + 8n + 8 + 64M - 8n - 9

where M=n+1C2+8n+1C3++8n1M = {}^{n+1}C_2 + 8\cdot{}^{n+1}C_3 + \cdots + 8^{n-1} is a positive integer.

=64M= 64M

Hence 9n+18n99^{n+1}-8n-9 is divisible by 64 for every positive integer nn. \blacksquare
14Prove that r=0n3rnCr=4n\displaystyle\sum_{r=0}^{n} 3^r\,{}^nC_r = 4^n.Show solution
We use the Binomial Theorem:

(1+x)n=r=0nnCrxr(1+x)^n = \sum_{r=0}^{n}{}^nC_r\, x^r

Substitute x=3x = 3:

(1+3)n=r=0nnCr3r(1+3)^n = \sum_{r=0}^{n}{}^nC_r\, 3^r

4n=r=0n3rnCr4^n = \sum_{r=0}^{n} 3^r\,{}^nC_r

Hence proved. \blacksquare

Miscellaneous Exercise on Chapter 7

1If aa and bb are distinct integers, prove that aba-b is a factor of anbna^n - b^n, whenever nn is a positive integer. [Hint: write an=(ab+b)na^n = (a-b+b)^n and expand]Show solution
Proof:

Write a=(ab)+ba = (a-b)+b. Then:

an=[(ab)+b]n=r=0nnCr(ab)rbnra^n = [(a-b)+b]^n = \sum_{r=0}^{n}{}^nC_r(a-b)^r\, b^{n-r}

=nC0bn+nC1(ab)bn1+nC2(ab)2bn2++nCn(ab)n= {}^nC_0\, b^n + {}^nC_1(a-b)b^{n-1} + {}^nC_2(a-b)^2 b^{n-2} + \cdots + {}^nC_n(a-b)^n

=bn+(ab)[nC1bn1+nC2(ab)bn2++(ab)n1]= b^n + (a-b)\left[{}^nC_1 b^{n-1} + {}^nC_2(a-b)b^{n-2} + \cdots + (a-b)^{n-1}\right]

Therefore:

anbn=(ab)[nC1bn1+nC2(ab)bn2++(ab)n1]a^n - b^n = (a-b)\left[{}^nC_1 b^{n-1} + {}^nC_2(a-b)b^{n-2} + \cdots + (a-b)^{n-1}\right]

The expression in brackets is an integer (since aa and bb are integers). Hence (ab)(a-b) is a factor of anbna^n - b^n. \blacksquare
2Evaluate (3+2)6(32)6(\sqrt{3}+\sqrt{2})^6-(\sqrt{3}-\sqrt{2})^6.Show solution
Let a=3a=\sqrt{3}, b=2b=\sqrt{2}.

Expand (a+b)6(a+b)^6 and (ab)6(a-b)^6:

(a+b)6=a6+6a5b+15a4b2+20a3b3+15a2b4+6ab5+b6(a+b)^6 = a^6+6a^5b+15a^4b^2+20a^3b^3+15a^2b^4+6ab^5+b^6

(ab)6=a66a5b+15a4b220a3b3+15a2b46ab5+b6(a-b)^6 = a^6-6a^5b+15a^4b^2-20a^3b^3+15a^2b^4-6ab^5+b^6

Subtracting:

(a+b)6(ab)6=2[6a5b+20a3b3+6ab5]=2ab[6a4+20a2b2+6b4](a+b)^6-(a-b)^6 = 2\left[6a^5b+20a^3b^3+6ab^5\right] = 2ab\left[6a^4+20a^2b^2+6b^4\right]

Now substitute a=3a=\sqrt{3}, b=2b=\sqrt{2}, so ab=6ab=\sqrt{6}, a2=3a^2=3, b2=2b^2=2:

=26[6(9)+20(3)(2)+6(4)]= 2\sqrt{6}\left[6(9)+20(3)(2)+6(4)\right]

=26[54+120+24]= 2\sqrt{6}\left[54+120+24\right]

=26×198=3966= 2\sqrt{6}\times198 = 396\sqrt{6}

(3+2)6(32)6=3966\boxed{(\sqrt{3}+\sqrt{2})^6-(\sqrt{3}-\sqrt{2})^6 = 396\sqrt{6}}
3Find the value of (a2+a21)4+(a2a21)4\left(a^2+\sqrt{a^2-1}\right)^4+\left(a^2-\sqrt{a^2-1}\right)^4.Show solution
Let x=a2x = a^2 and y=a21y = \sqrt{a^2-1}.

Expand (x+y)4(x+y)^4 and (xy)4(x-y)^4:

(x+y)4+(xy)4=2[4C0x4+4C2x2y2+4C4y4](x+y)^4+(x-y)^4 = 2\left[{}^4C_0 x^4 + {}^4C_2 x^2 y^2 + {}^4C_4 y^4\right]

=2[x4+6x2y2+y4]= 2\left[x^4 + 6x^2y^2 + y^4\right]

Substitute back x=a2x=a^2, y2=a21y^2 = a^2-1:

=2[(a2)4+6(a2)2(a21)+(a21)2]= 2\left[(a^2)^4 + 6(a^2)^2(a^2-1) + (a^2-1)^2\right]

=2[a8+6a4(a21)+(a42a2+1)]= 2\left[a^8 + 6a^4(a^2-1) + (a^4-2a^2+1)\right]

=2[a8+6a66a4+a42a2+1]= 2\left[a^8 + 6a^6 - 6a^4 + a^4 - 2a^2 + 1\right]

=2[a8+6a65a42a2+1]= 2\left[a^8 + 6a^6 - 5a^4 - 2a^2 + 1\right]

=2a8+12a610a44a2+2\boxed{= 2a^8 + 12a^6 - 10a^4 - 4a^2 + 2}
4Find an approximation of (0.99)5(0.99)^5 using the first three terms of its expansion.Show solution
Write: 0.99=10.010.99 = 1 - 0.01

(0.99)5=(10.01)5(0.99)^5 = (1-0.01)^5

Using the first three terms of the binomial expansion:

5C0(1)5+5C1(1)4(0.01)+5C2(1)3(0.01)2\approx {}^5C_0(1)^5 + {}^5C_1(1)^4(-0.01) + {}^5C_2(1)^3(-0.01)^2

=1+5×(0.01)+10×(0.0001)= 1 + 5\times(-0.01) + 10\times(0.0001)

=10.05+0.001= 1 - 0.05 + 0.001

(0.99)50.951\boxed{(0.99)^5 \approx 0.951}
5Expand using Binomial Theorem (1+x22x)4,  x0\left(1+\dfrac{x}{2}-\dfrac{2}{x}\right)^4,\; x\neq 0.Show solution
Strategy: Group as [(1+x2)2x]4\left[\left(1+\dfrac{x}{2}\right)-\dfrac{2}{x}\right]^4 and let p=1+x2p = 1+\dfrac{x}{2}, q=2xq = \dfrac{2}{x}.

(pq)4=4C0p44C1p3q+4C2p2q24C3pq3+4C4q4(p-q)^4 = {}^4C_0 p^4 - {}^4C_1 p^3 q + {}^4C_2 p^2 q^2 - {}^4C_3 p q^3 + {}^4C_4 q^4

Compute each part:

p=1+x2p = 1+\dfrac{x}{2}, q=2xq = \dfrac{2}{x}

p2=1+x+x24p^2 = 1 + x + \dfrac{x^2}{4}

p3=(1+x2)3=1+3x2+3x24+x38p^3 = \left(1+\dfrac{x}{2}\right)^3 = 1 + \dfrac{3x}{2} + \dfrac{3x^2}{4} + \dfrac{x^3}{8}

p4=(1+x2)4=1+2x+3x22+x32+x416p^4 = \left(1+\dfrac{x}{2}\right)^4 = 1 + 2x + \dfrac{3x^2}{2} + \dfrac{x^3}{2} + \dfrac{x^4}{16}

q2=4x2q^2 = \dfrac{4}{x^2}, q3=8x3q^3 = \dfrac{8}{x^3}, q4=16x4q^4 = \dfrac{16}{x^4}

Term 1: p4=1+2x+3x22+x32+x416p^4 = 1+2x+\dfrac{3x^2}{2}+\dfrac{x^3}{2}+\dfrac{x^4}{16}

Term 2: 4p3q=4(1+3x2+3x24+x38)2x-4p^3 q = -4\left(1+\dfrac{3x}{2}+\dfrac{3x^2}{4}+\dfrac{x^3}{8}\right)\cdot\dfrac{2}{x}
=8x(1+3x2+3x24+x38)= -\dfrac{8}{x}\left(1+\dfrac{3x}{2}+\dfrac{3x^2}{4}+\dfrac{x^3}{8}\right)
=8x126xx2= -\dfrac{8}{x} - 12 - 6x - x^2

Term 3: 6p2q2=6(1+x+x24)4x26p^2 q^2 = 6\left(1+x+\dfrac{x^2}{4}\right)\cdot\dfrac{4}{x^2}
=24x2(1+x+x24)= \dfrac{24}{x^2}\left(1+x+\dfrac{x^2}{4}\right)
=24x2+24x+6= \dfrac{24}{x^2}+\dfrac{24}{x}+6

Term 4: 4pq3=4(1+x2)8x3-4p q^3 = -4\left(1+\dfrac{x}{2}\right)\cdot\dfrac{8}{x^3}
=32x3(1+x2)= -\dfrac{32}{x^3}\left(1+\dfrac{x}{2}\right)
=32x316x2= -\dfrac{32}{x^3}-\dfrac{16}{x^2}

Term 5: q4=16x4q^4 = \dfrac{16}{x^4}

Adding all terms:

(1+x22x)4=16x432x3+24x232x2+24x8x12+6+1+2xx2+3x226x+x32+x416\left(1+\frac{x}{2}-\frac{2}{x}\right)^4 = \frac{16}{x^4} - \frac{32}{x^3} + \frac{24}{x^2} - \frac{32}{x^2} + \frac{24}{x} - \frac{8}{x} - 12 + 6 + 1 + 2x - x^2 + \frac{3x^2}{2} - 6x + \frac{x^3}{2} + \frac{x^4}{16}

Collecting like powers:

- x4x^4: x416\dfrac{x^4}{16}
- x3x^3: x32\dfrac{x^3}{2}
- x2x^2: x2+3x22=x22-x^2+\dfrac{3x^2}{2} = \dfrac{x^2}{2}
- x1x^1: 2x6x=4x2x-6x = -4x
- x0x^0: 12+6+1=5-12+6+1 = -5
- x1x^{-1}: 24x8x=16x\dfrac{24}{x}-\dfrac{8}{x} = \dfrac{16}{x}
- x2x^{-2}: 24x216x2=8x2\dfrac{24}{x^2}-\dfrac{16}{x^2} = \dfrac{8}{x^2}
- x3x^{-3}: 32x3-\dfrac{32}{x^3}
- x4x^{-4}: 16x4\dfrac{16}{x^4}

(1+x22x)4=x416+x32+x224x5+16x+8x232x3+16x4\boxed{\left(1+\frac{x}{2}-\frac{2}{x}\right)^4 = \frac{x^4}{16}+\frac{x^3}{2}+\frac{x^2}{2}-4x-5+\frac{16}{x}+\frac{8}{x^2}-\frac{32}{x^3}+\frac{16}{x^4}}
6Find the expansion of (3x22ax+3a2)3(3x^2-2ax+3a^2)^3 using binomial theorem.Show solution
Strategy: Write 3x22ax+3a2=(3x22ax)+3a23x^2-2ax+3a^2 = (3x^2-2ax)+3a^2 and apply the Binomial Theorem with p=3x22axp = 3x^2-2ax and q=3a2q = 3a^2.

(p+q)3=p3+3p2q+3pq2+q3(p+q)^3 = p^3 + 3p^2q + 3pq^2 + q^3

Compute each part:

p=3x22axp = 3x^2-2ax, q=3a2q = 3a^2

p2=(3x22ax)2=9x412ax3+4a2x2p^2 = (3x^2-2ax)^2 = 9x^4 - 12ax^3 + 4a^2x^2

p3=(3x22ax)3p^3 = (3x^2-2ax)^3

Expand p3p^3 using Binomial Theorem:
(3x22ax)3=(3x2)33(3x2)2(2ax)+3(3x2)(2ax)2(2ax)3(3x^2-2ax)^3 = (3x^2)^3 - 3(3x^2)^2(2ax) + 3(3x^2)(2ax)^2 - (2ax)^3
=27x639x42ax+33x24a2x28a3x3= 27x^6 - 3\cdot9x^4\cdot2ax + 3\cdot3x^2\cdot4a^2x^2 - 8a^3x^3
=27x654ax5+36a2x48a3x3= 27x^6 - 54ax^5 + 36a^2x^4 - 8a^3x^3

3p2q=3(9x412ax3+4a2x2)(3a2)3p^2q = 3(9x^4-12ax^3+4a^2x^2)(3a^2)
=9a2(9x412ax3+4a2x2)= 9a^2(9x^4-12ax^3+4a^2x^2)
=81a2x4108a3x3+36a4x2= 81a^2x^4 - 108a^3x^3 + 36a^4x^2

3pq2=3(3x22ax)(9a4)3pq^2 = 3(3x^2-2ax)(9a^4)
=27a4(3x22ax)= 27a^4(3x^2-2ax)
=81a4x254a5x= 81a^4x^2 - 54a^5x

q3=(3a2)3=27a6q^3 = (3a^2)^3 = 27a^6

Adding all terms:

=27x654ax5+(36a2+81a2)x4+(8a3108a3)x3+(36a4+81a4)x254a5x+27a6= 27x^6 - 54ax^5 + (36a^2+81a^2)x^4 + (-8a^3-108a^3)x^3 + (36a^4+81a^4)x^2 - 54a^5x + 27a^6

(3x22ax+3a2)3=27x654ax5+117a2x4116a3x3+117a4x254a5x+27a6\boxed{(3x^2-2ax+3a^2)^3 = 27x^6 - 54ax^5 + 117a^2x^4 - 116a^3x^3 + 117a^4x^2 - 54a^5x + 27a^6}

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