Introduction to Linear Polynomials
CBSE · Class 9 · Mathematics
NCERT Solutions for Introduction to Linear Polynomials — CBSE Class 9 Mathematics.
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EXERCISE SET 2.1
1(i)Show solution
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1(ii)Show solution
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1(iii)Show solution
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1(iv)Show solution
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2Write polynomials of degrees 1, 2 and 3.Show solution
- Degree 1:
- Degree 2:
- Degree 3:
Any valid polynomials of these degrees are acceptable.
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3What are the coefficients of and in the polynomial ?Show solution
- The coefficient of is 6.
- The coefficient of is -3.
So the required coefficients are and .
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4What is the coefficient of in the polynomial ?Show solution
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5What is the constant term of the polynomial ?Show solution
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EXERCISE SET 2.2
1(i)Show solution
.
So the value is -3.
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1(ii)Show solution
.
So the value is -8.
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1(iii)Show solution
.
So the value is 7.
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2(i)Show solution
.
So the value is 6.
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2(ii)Show solution
.
So the value is 81.
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2(iii)Show solution
.
So the value is 102.
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3The present age of Salil's mother is three times Salil's present age. After 5 years, their ages will add up to 70 years. Find their present ages.Show solution
After 5 years:
- Salil's age =
- Mother's age =
Their sum is 70:
So Salil is 15 years old and his mother is 45 years old.
But this does not match the book's worked setup in the chapter excerpt? No, using the stated relation gives these ages.
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4The difference between two positive integers is 63. The ratio of the two integers is 2:5. Find the two integers.Show solution
So, let them be and .
Their difference is 63:
So the integers are:
and .
Thus, the two integers are 42 and 105.
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5Ruby has 3 times as many two-rupee coins as she has five rupee-coins. If she has a total ₹88, how many coins does she have of each type?Show solution
Then the number of two-rupee coins is .
Total value:
So:
- five-rupee coins =
- two-rupee coins =
Thus, she has 24 two-rupee coins and 8 five-rupee coins.
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6A farmer cuts a 300 feet fence into two pieces of different sizes. The longer piece is four times as long as the shorter piece. How long are the two pieces?Show solution
Total length is 300 ft:
So the two pieces are:
- shorter piece = 60 ft
- longer piece = 240 ft
So the lengths are 60 ft and 240 ft.
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7If the length of a rectangle is three more than twice its width and its perimeter is 24 cm, what are the dimensions of the rectangle?Show solution
Then length = cm.
Perimeter of rectangle = 24 cm:
Then length = cm.
So the dimensions are 3 cm by 9 cm.
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1Find the value of the linear polynomial if:Show solution
- If , then .
- If , then .
- If , then .
So the values are -3, -8, 7.
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2Find the value of the quadratic polynomial if:Show solution
- If , value = .
- If , value = .
- If , value = .
So the values are 6, 81, 102.
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EXERCISE SET 2.3
1A student has ₹500 in her savings bank account. She gets ₹150 every month as pocket money. How much money will she have at the end of every month from the second month onwards? Find a linear expression to represent the amount she will have in the month.Show solution
She starts with ₹500 and gets ₹150 each month, so:
Thus:
- 1st month: ₹650
- 2nd month: ₹800
- 3rd month: ₹950
- 4th month: ₹1100
- and so on.
The required linear expression is ****.
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2A rally starts with 120 members. Each hour, 9 members drop out of the group. How many members will remain after 1, 2, 3, ... hours? Find a linear expression to represent the number of members at the end of the nth hour.Show solution
So after hours, the number of members is
The first few values are:
- after 1 hour:
- after 2 hours:
- after 3 hours:
So the linear expression is ****.
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3Suppose the length of a rectangle is 13 cm. Find the area if the breadth is (i) 12 cm, (ii) 10 cm, (iii) 8 cm. Find the linear pattern representing the area of the rectangle.Show solution
- If breadth = 12 cm, area = cm²
- If breadth = 10 cm, area = cm²
- If breadth = 8 cm, area = cm²
So the linear pattern is:
and the expression for area is ****.
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4Suppose the length of a rectangular box is 7 cm and breadth is 11 cm. Find the volume if the height is (i) 5 cm, (ii) 9 cm, (iii) 13 cm. Find the linear pattern representing the volume of the rectangular box.Show solution
- If cm, volume = cm³
- If cm, volume = cm³
- If cm, volume = cm³
So the linear pattern is:
and the expression is ****.
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5Sarita is reading a book of 500 pages. She reads 20 pages every day. How many pages will be left after 15 days? Express this as a linear pattern.Show solution
pages.
Pages left after 15 days:
So the linear pattern for pages left is
or, after days,
Thus after 15 days, 200 pages will be left.
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3Suppose the length of a rectangle is 13 cm. Find the area if the breadth isShow solution
Area of a rectangle = length × breadth.
- If breadth = cm, area =
- If breadth = cm, area =
- If breadth = cm, area =
So the linear pattern for the area is:
and in general, if breadth is , then area is
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4Suppose the length of a rectangular box is 7 cm and breadth is 11 cm. Find the volume if the height isShow solution
Volume of a rectangular box = length × breadth × height.
First find the base area:
Now multiply by the height:
- If height = cm, volume =
- If height = cm, volume =
- If height = cm, volume =
So the linear pattern for the volume is:
and in general, if height is , then
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EXERCISE SET 2.4
1(i)Find the height after 7 months.Show solution
After 7 months, height =
But the question asks for the source exercise answer, which in the chapter is based on a plant growth example with the same pattern. For this specific item, the height after 7 months is 5.25 feet.
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1(ii)Make a table of values for t varying from 0 to 10 months and show how the height, h, increases every month.Show solution
So for months,
The table of values from to is:
| | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| (feet) | 1.75 | 2.25 | 2.75 | 3.25 | 3.75 | 4.25 | 4.75 | 5.25 | 5.75 | 6.25 | 6.75 |
Each month the height increases by a constant amount of 0.5 feet, so this is a linear growth pattern.
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1(iii)Find an expression that relates h and t, and explain why it represents linear growth.Show solution
Here, is the initial height and is the fixed amount added each month.
This represents linear growth because the height increases by the same amount, feet, over each equal interval of one month. Since the rate of increase is constant, the relation is linear.
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2(i)Find the value of the phone after 3 years.Show solution
After 3 years:
So the value of the phone after 3 years is ₹7600.
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2(ii)Make a table of values for t varying from 0 to 8 years and show how the value of the phone, v, depreciates with time.Show solution
So the values from to years are:
| (years) | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|---|---|
| (₹) | 10000 | 9200 | 8400 | 7600 | 6800 | 6000 | 5200 | 4400 | 3600 |
The value decreases by a constant amount of ₹800 each year, so it shows linear decay.
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2(iii)Find an expression that relates v and t, and explain why it represents linear decay.Show solution
This represents linear decay because the value decreases by a fixed amount, ₹800, in each equal time interval of one year. The decrease is constant, so the graph is linear with negative slope.
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3(i)Find the population of the village after 6 years.Show solution
After 6 years:
So the population after 6 years is 1050.
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3(ii)Make a table of values for t varying from 0 to 10 years and show how the population, P, increases every year.Show solution
So the population after years is:
Now make the table for to :
| (years) | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| | 750 | 800 | 850 | 900 | 950 | 1000 | 1050 | 1100 | 1150 | 1200 | 1250 |
This shows that the population increases by 50 every year.
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3(iii)Find an expression that relates P and t, and explain why it represents linear growth.Show solution
Each year, 50 people move to the village, so the population increases by 50 every year.
Therefore, the expression relating population and time is:
This represents linear growth because the population increases by a constant amount of 50 for each equal interval of 1 year.
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4(i)Write an equation that models the remaining balance b(x) after using the scheme for x days. Explain why it represents linear decay.Show solution
Each day, the balance is reduced by ₹15.
So after days, the remaining balance is:
This represents linear decay because the balance decreases by the same constant amount of ₹15 every day.
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4(ii)After how many days will the balance run out?Show solution
Given
Set it equal to zero:
So, the balance will run out after 40 days.
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4(iii)Make a table of values for x varying from 1 to 10 days and show how the balance b(x), reduces with time.Show solution
So,
Now find values for to :
| (days) | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|
| (₹) | 585 | 570 | 555 | 540 | 525 | 510 | 495 | 480 | 465 | 450 |
This table shows that the balance reduces by 15 each day.
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1Suppose a plant has height 1.75 feet and it grows by 0.5 feet each month.Show solution
So after months, its height is:
For :
feet
Table of values for to :
| (months) | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| (feet) | 1.75 | 2.25 | 2.75 | 3.25 | 3.75 | 4.25 | 4.75 | 5.25 | 5.75 | 6.25 | 6.75 |
The expression is a linear growth pattern because the height increases by a constant amount of 0.5 feet every month.
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2A mobile phone is bought for ₹10,000. Its value decreases by ₹800 every year.Show solution
So after years, the value is:
For the required values:
- After 3 years:
Table for to :
| (years) | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 |
|---|---|---|---|---|---|---|---|---|---|
| (₹) | 10000 | 9200 | 8400 | 7600 | 6800 | 6000 | 5200 | 4400 | 3600 |
This is linear decay because the value decreases by a constant amount of ₹800 every year.
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3The initial population of a village is 750. Every year, 50 people move from a nearby city to the village.Show solution
So after years, the population is:
For the required year:
- After 6 years:
Table for to :
| (years) | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| | 750 | 800 | 850 | 900 | 950 | 1000 | 1050 | 1100 | 1150 | 1200 | 1250 |
This is linear growth because the population increases by the same amount, 50, every year.
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EXERCISE SET 2.5
1A learning platform charges a fixed monthly fee and an additional cost per digital learning module accessed. A student observes that when she accessed 10 modules, her bill was ₹400. When she accessed 14 modules, her bill was ₹500. If the monthly bill depends on the number of modules accessed, , according to the relation , find the values of and .Show solution
Given points:
- When ,
- When ,
So,
Subtract the first equation from the second:
Now substitute in :
So, ** and **.
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2A gym charges a fixed monthly fee and an additional cost per hour for using the badminton court. A student using the gym observed that when she used the badminton court for 10 hours, her bill was ₹800. When she used it for 15 hours, her bill was ₹1100. If the monthly bill depends on the hours of the use of the badminton court, , according to the relation , find the values of and .Show solution
Given:
- When ,
- When ,
So,
Subtract the first equation from the second:
Now substitute into :
So, ** and **.
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3Consider the relationship between temperature measured in degrees Celsius (°C) and degrees Fahrenheit (°F), which is given by °C = °F + . Find and , given that ice melts at 0 degrees Celsius and 32 degrees Fahrenheit, and water boils at 100 degrees Celsius and 212 degrees Fahrenheit.Show solution
Using the two given points:
- When , :
- When , :
Subtract the first equation from the second:
So,
Now substitute in :
So the linear relation is
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3Consider the relationship between temperature measured in degrees Celsius (°C) and degrees Fahrenheit (°F), which is given by °C = °F + . Find and , given that ice melts at 0 degrees Celsius and 32 degrees Fahrenheit, and water boils at 100 degrees Celsius and 212 degrees Fahrenheit.
(Hint: When °C = 0, °F = 32 and when °C = 100, °F = 212. Use this information to find and , and thus, the linear relationship between °C and °F.)Show solution
From the data:
- Ice melts: , gives
- Water boils: , gives
Subtracting the first equation from the second:
Hence,
Now substitute into :
So, the values are and .
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Think and Reflect
1Can you identify the terms, variables and coefficients of this algebraic expression?Show solution
the terms are:
-
-
-
The variables are:
-
-
The coefficients are:
- of , the coefficient is
- of , the coefficient is
- of , the coefficient is
So the expression has three terms, two variables, and coefficients 200, 160, and 50.
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EXERCISE SET 2.6
END-OF-CHAPTER EXERCISES
- (i) .
- (ii) The polynomial cuts the x-axis at (3, 0).
- (iii) The sum is equal to for all real .
Find the polynomials and .
(i) The graph of passes through the points (2, 3) and (6, 11).
(ii) The graph of passes through the point (4, -1).
(iii) The graph of is parallel to the graph of .
Find the polynomials and . Also, find the coordinates of the point where these lines meet the x-axis.
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