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Chapter 7 of 14
NCERT Solutions

Binomial Theorem

Madhya Pradesh Board · Class 11 · Mathematics

NCERT Solutions for Binomial Theorem — Madhya Pradesh Board Class 11 Mathematics.

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20 Questions Solved · 2 Sections

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EXERCISE 7.1

1(12x)5(1 - 2x)^5Show solution
Using the binomial theorem,
(12x)5=r=055Cr(1)5r(2x)r. (1-2x)^5=\sum_{r=0}^{5} {^5C_r}(1)^{5-r}(-2x)^r.
Now compute term by term:
=15(2x)+10(2x)210(2x)3+5(2x)4(2x)5. =1-5(2x)+10(2x)^2-10(2x)^3+5(2x)^4-(2x)^5.
So,
(12x)5=110x+40x280x3+80x432x5. (1-2x)^5=1-10x+40x^2-80x^3+80x^4-32x^5.

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2(2xx2)5\left(\frac{2}{x} - \frac{x}{2}\right)^5Show solution
Using the binomial theorem,
(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.
Compute each term:
=(2x)55(2x)4(x2)+10(2x)3(x2)2 =\left(\frac{2}{x}\right)^5-5\left(\frac{2}{x}\right)^4\left(\frac{x}{2}\right)+10\left(\frac{2}{x}\right)^3\left(\frac{x}{2}\right)^2
10(2x)2(x2)3+5(2x)(x2)4(x2)5. -10\left(\frac{2}{x}\right)^2\left(\frac{x}{2}\right)^3+5\left(\frac{2}{x}\right)\left(\frac{x}{2}\right)^4-\left(\frac{x}{2}\right)^5.
Simplifying,
=32x540x3+20x5x+5x316x532. =\frac{32}{x^5}-\frac{40}{x^3}+\frac{20}{x}-5x+\frac{5x^3}{16}-\frac{x^5}{32}.

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3(2x3)6(2x - 3)^6Show solution
Using the binomial theorem,
(2x3)6=r=066Cr(2x)6r(3)r. (2x-3)^6=\sum_{r=0}^{6} {^6C_r}(2x)^{6-r}(-3)^r.
Now expand term by term:
(2x)66(2x)5(3)+15(2x)4(32)20(2x)3(33)+15(2x)2(34)6(2x)(35)+36. (2x)^6-6(2x)^5(3)+15(2x)^4(3^2)-20(2x)^3(3^3)+15(2x)^2(3^4)-6(2x)(3^5)+3^6.
So,
(2x3)6=64x6576x5+2160x44320x3+4860x22916x+729. (2x-3)^6=64x^6-576x^5+2160x^4-4320x^3+4860x^2-2916x+729.

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4(x3+1x)5\left(\frac{x}{3} + \frac{1}{x}\right)^5Show solution
Using the binomial theorem,
(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.
Compute the terms:
=(x3)5+5(x3)41x+10(x3)31x2+10(x3)21x3+5(x3)1x4+1x5. =\left(\frac{x}{3}\right)^5+5\left(\frac{x}{3}\right)^4\frac{1}{x}+10\left(\frac{x}{3}\right)^3\frac{1}{x^2}+10\left(\frac{x}{3}\right)^2\frac{1}{x^3}+5\left(\frac{x}{3}\right)\frac{1}{x^4}+\frac{1}{x^5}.
Simplifying,
(x3+1x)5=x5243+5x381+10x27+103x+5x3+1x5. \left(\frac{x}{3}+\frac{1}{x}\right)^5=\frac{x^5}{243}+\frac{5x^3}{81}+\frac{10x}{27}+\frac{10}{3x}+\frac{5}{x^3}+\frac{1}{x^5}.

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5(x+1x)6\left(x + \frac{1}{x}\right)^6Show solution
Using the binomial theorem,
(x+1x)6=r=066Crx6r(1x)r. \left(x+\frac{1}{x}\right)^6=\sum_{r=0}^{6}{^6C_r}x^{6-r}\left(\frac{1}{x}\right)^r.
So,
=x6+6x4+15x2+20+15x2+6x4+x6. = x^6+6x^4+15x^2+20+15x^{-2}+6x^{-4}+x^{-6}.
Hence,
(x+1x)6=x6+6x4+15x2+20+15x2+6x4+1x6. \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}.

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6(96)3(96)^3Show solution

963=(1004)3 96^3=(100-4)^3
Using (ab)3=a33a2b+3ab2b3(a-b)^3=a^3-3a^2b+3ab^2-b^3,
(1004)3=1003310024+31004243. (100-4)^3=100^3-3\cdot100^2\cdot4+3\cdot100\cdot4^2-4^3.
=1000000120000+480064=884736. =1000000-120000+4800-64=884736.

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7(102)5(102)^5Show solution

1025=(100+2)5 102^5=(100+2)^5
Using the binomial theorem,
(100+2)5=1005+510042+10100322+10100223+510024+25. (100+2)^5=100^5+5\cdot100^4\cdot2+10\cdot100^3\cdot2^2+10\cdot100^2\cdot2^3+5\cdot100\cdot2^4+2^5.
Now calculate:
1005=10000000000, 100^5=10000000000,
510042=1000000000, 5\cdot100^4\cdot2=1000000000,
1010034=40000000, 10\cdot100^3\cdot4=40000000,
1010028=800000, 10\cdot100^2\cdot8=800000,
510016=8000, 5\cdot100\cdot16=8000,
25=32. 2^5=32.
Adding,
10000000000+1000000000+40000000+800000+8000+32=11040808032. 10000000000+1000000000+40000000+800000+8000+32=11040808032.
So the value is 1104080803211040808032.

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8(101)4(101)^4Show solution

1014=(100+1)4 101^4=(100+1)^4
Using (a+b)4=a4+4a3b+6a2b2+4ab3+b4(a+b)^4=a^4+4a^3b+6a^2b^2+4ab^3+b^4,
(100+1)4=1004+41003+61002+4100+1. (100+1)^4=100^4+4\cdot100^3+6\cdot100^2+4\cdot100+1.
=100000000+4000000+60000+400+1=104060401. =100000000+4000000+60000+400+1=104060401.

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9(99)5(99)^5Show solution

995=(1001)5 99^5=(100-1)^5
Using the binomial theorem,
(1001)5=100551004+101003101002+51001. (100-1)^5=100^5-5\cdot100^4+10\cdot100^3-10\cdot100^2+5\cdot100-1.
Now compute:
1005=10000000000, 100^5=10000000000,
51004=500000000, 5\cdot100^4=500000000,
101003=10000000, 10\cdot100^3=10000000,
101002=100000, 10\cdot100^2=100000,
5100=500. 5\cdot100=500.
So,
10000000000500000000+10000000100000+5001=950990049. 10000000000-500000000+10000000-100000+500-1=950990049.

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10Using Binomial Theorem, indicate which number is larger (1.1)10000(1.1)^{10000} or 1000.Show solution
Using the binomial theorem,
(1.1)10000=(1+0.1)10000. (1.1)^{10000}=(1+0.1)^{10000}.
All terms in the expansion are positive, so
(1+0.1)10000>1+10000(0.1)=1001. (1+0.1)^{10000} > 1 + 10000(0.1)=1001.
Therefore,
(1.1)10000>1000. (1.1)^{10000} > 1000.
So (1.1)^{10000} is larger.

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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.
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.
13Show that 9n+18n99^{n+1} - 8n - 9 is divisible by 64, whenever nn is a positive integer.
14Prove that r=0n3rnCr=4n\sum_{r=0}^n 3^r {}^nC_r = 4^n.

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.
2Evaluate (3+2)6(32)6(\sqrt{3} + \sqrt{2})^6 - (\sqrt{3} - \sqrt{2})^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.
4Find an approximation of (0.99)5(0.99)^5 using the first three terms of its expansion.
5Expand using Binomial Theorem (1+x22x)4,x0\left(1 + \frac{x}{2} - \frac{2}{x}\right)^4, x \neq 0.
6Find the expansion of (3x22ax+3a2)3(3x^2 - 2ax + 3a^2)^3 using binomial theorem.

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Binomial Theorem covers several key topics that are frequently asked in Madhya Pradesh Board Class 11 board exams. Focus on the core concepts listed on this page and practise related questions to build confidence.
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