Exercise 2C RS Aggarwal Class 9

Exercise 2C RS Aggarwal Class 9 contains a total of sixteen questions. The questions are based on the following topics.

  • Division Algorithm in Polynomials
  • Remainder Theorem

Exercise 2C RS Aggarwal Class 9 Mathematics Solutions

The first question in Exercise 2C RS Aggarwal Class 9 asks us to find the quotient and remainder by doing actual division.

1. By actual division, find the quotient and the remainder when (x4+1) is divided by (x1).
Verify that remainder = f(1).

Exercise 2A RS Aggarwal Class 9 Question 1 Actual Division

From the above division, we see that remainder when (x4+1) is divided by (x+1) is 2 and quotient is x3+x2+x+1.

Verification:
f (x )=x4+1
Putting x=1, we get.
f(1)=14+1=1+1=2.
Hence, verified!

The second question of Exercise 2C RS Aggarwal Class 9 asks us to verify the division algorithm for the polynomials.

2. Verify the division algorithm for the polynomials
p(x)=2x46x3+2x2x+2 and g(x)=x+2.

Given polynomials are
p(x)=2x46x3+2x2x+2 and g(x)=x+2.

Exercise 2C RS Aggarwal Class 9 Question 2 Division Algorithm for the polynomials

After dividing p(x) by g(x), we get.
Quotient q(x) = 2x310x2+22x45
Remainder r(x) = 92

Verification of Division Algorithm:

To verify: Dividend=Divisor×Quotient+Remainder
i.e. p(x)=g(x)×q(x)+r(x)

Taking Right Hand Side (RHS), we have,
Divisor×Quotient+Remainder
=(x+2)×(2x310x2+22x45)+92
=[x(2x310x2+22x45)+2(2x310x2+22x45)]+92
=2x410x3+22x245x+4x320x2+44x90+92
=2x46x3+2x2x+2
= p(x) Dividend.
Hence, verified!

The questions from third to twelfth from Exercise 2C RS Aggarwal Class 9 asks us to use remainder theorem to find remainder.

Using the remainder theorem, find the remainder, when p(x) is divided by g(x), where

3. p(x)=x36x2+9x+3, g(x)=x1

We have
p(x)=x36x2+9x+3, g(x)=x1.
Here, g(x) = 0
x1=0
x=1

According to remainder theorem, when p(x) is divided by g(x), the remainder is p(1).

 p(x)=x36x2+9x+3
p(1)=136×12+9×1+3
p(1)=16+9+3
p(1)=7

Hence, the remainder when p(x) is divided by g(x) is 7.

4. p(x)=2x37x2+9x13, g(x)=x3

We have
p(x)=2x37x2+9x13, g(x)=x3
Here, g(x)=0
x3=0
x=3

According to remainder theorem, when p(x) is divided by g(x), the remainder is p(3).

 p(x)=2x37x2+9x-13
p(3)=2×337×32+9×313
p(3)=5463+2713
p(3)=5.

Hence, the remainder when p(x) is divided by g(x) is 5.

5. p(x)=3x46x28x2, g(x)=x2

We have
p(x)=3x46x28x2, g(x)=x2
Here, g(x)=0
x2=0
x=2.

According to remainder theorem, when p(x) is divided by g(x), the remainder is p(2).

 p(x)=3x46x28x-2
p(2)=3×246×228×22
p(2)=4824162
p(2)=6.

Hence, the remainder when p(x) is divided by g(x) is 6.

6. p(x)=2x39x2+x+15, g(x)=2x3

We have
p(x)=2x39x2+x+15, g(x)=2x3
Here, g(x)=0
2x3=0
x=32

According to remainder theorem, when p(x) is divided by g(x), the remainder is p(32).

 p(x)=2x39x2+x+15
p(32)=2(32)39(32)2+(32)+15
p(32)=2×2789×94+32+15
p(32)=274814+32+15
p(32)=2781+6+604=124=3.

Hence, the remainder when p(x) is divided by g(x) is 3.

7. p(x)=x32x28x1, g(x)=x+1.

We have
p(x)=x32x28x1, g(x)=x+1.
Here, g(x)=0
x+1=0
x=1.

According to remainder theorem, when p(x) is divided by g(x), the remainder is p(1).

 p(x)=x32x28x1
p(1)=(1)32×(1)28×(1)1
p(1)=-12+81
p(1)=4.

Hence, the remainder when p(x) is divided by g(x) is 4.

8. p(x)=2x3+x215x12, g(x)=x+2.

We have
p(x)=2x3+x215x12, g(x)=x+2.
Here, g(x)=0
x+2=0
x=2.

According to remainder theorem, when p(x) is divided by g(x), the remainder is p(2).

 p(x)=2x3+x215x12
p(2)=2×(2)3+(2)215×(2)12
p(2)=-16+4+3012
p(2)=6.

Hence, the remainder when p(x) is divided by g(x) is 6.

9. p(x)=6x3+13x2+3, g(x)=3x+2.

We have
p(x)=6x3+13x2+3, g(x)=3x+2.
Here, g(x)=0
3x+2=0
x=23.

According to remainder theorem, when p(x) is divided by g(x), the remainder is p(23).

 p(x)=6x3+13x2+3
p(23)=6×(23)3+13×(23)2+3
p(23)=6×827+13×49+3
p(23)=169+529+3
p(23)=16+52+279
p(23)=639
p(23)=7.

Hence, the remainder when p(x) is divided by g(x) is 7.

10. p(x)=x36x2+2x4, g(x)=132x.

We have
p(x)=x36x2+2x4, g(x)=132x.
Here, g(x)=0
132x=0
32x=1
x=23.

According to remainder theorem, when p(x) is divided by g(x), the remainder is p(23).

 p(x)=x36x2+2x4
p(23)=(23)36×(23)2+2×(23)4
p(23)=8276×49+2×234
p(23)=82783+434
p(23)=872+3610827
p(23)=13627.

Hence, the remainder when p(x) is divided by g(x) is 13627.

11. p(x)=2x3+3x211x3, g(x)=(x+12).

We have
p(x)=2x3+3x211x3, g(x)=(x+12).
Here, g(x)=0
x+12=0
x=12

According to remainder theorem, when p(x) is divided by g(x), the remainder is p(12).

 p(x)=2x3+3x211x3
p(-12)=2×(-12)3+3×(-12)211×(-12)3
p(-12)=2×18+3×14+11×123
p(-12)=14+34+1123
p(-12)=1+3+22124
p(-12)=124
p(-12)=3

Hence, the remainder when p(x) is divided by g(x) is 3.

12. p(x)=x3ax2+6xa, g(x)=xa.

We have
p(x)=x3ax2+6xa, g(x)=xa.
Here, g(x)=0
xa=0
x=a.

According to remainder theorem, when p(x) is divided by g(x), the remainder is p(a).

 p(x)=x3ax2+6xa
p(a)=a3a×a2+6aa
p(a)=a3a3+6aa
x=5a.

Hence, the remainder when p(x) is divided by g(x) is 5a.

In Exercise 2C RS Aggarwal Class 9, the thirteenth question is a word problem on remainder theorem.

13. The polynomials (2x3+x2ax+2) and (2x33x23x+a) when divided by (x2) leave the same remainder. Find the value of a.

Let
p1(x)=2x3+x2ax+2 . . . (1) and
p2(x)=2x33x23x+a . . . (2)
g(x)=x2
Here, g(x)=0
x2=0
x=2.

According to remainder theorem, when p1(x) and p2(x) are divided by x2, the obtained remainders are p1(2) and p2(2) respectively.

Since the remainder obtained when p1(x) is divided by g(x) is equal to the remainder obtained when p2(x) is divided by g(x).
 p1(2)=p2(2)
2×23+222a+2=2×233×223×2+a
16+42a+2=16126+a
2aa=12624
3a=24
a=8.

Hence, the value of a is 8.

In Exercise 2C RS Aggarwal Class 9, the fourteenth question is a word problem that has been comprehensively solved below.

14. The polynomial p(x)=x42x3+3x2ax+b when divided by (x1) and (x+1) leaves the remainders 5 and 19 respectively. Find the values of a and b. Hence, find the remainder when p(x) is divided by (x2).

We have
p(x)=x42x3+3x2ax+b

 x1=0
x=1

According to remainder theorem, when p(x) is divided by (x1), the remainder is p(1).
 p(1)=5
142×13+3×12a×1+b=5
12+3a+b=5
2a+b=5
a+b=52
a+b=3 . . . (1)

Also, when p(x) is divided by (x+1), the remainder is p(1).
 p(1)=19
(1)42×(1)3+3×(1)2a×(1)+b=19
1+2+3+a+b=19
a+b=196
a+b=13 . . . (2)

Solving equations (1) and (2) by adding, we get.

a+b=3
  a+b=13
2b=16
b=8

putting b=8 in equation (2), we get.
a+8=13
a=138
a=5

Putting the values of a and b in p(x), we get.
 p(x)=x42x3+3x25x+8.

Now, the remainder when p(x) is divided by (x2) is p(2).
 p(2)=242×23+3×225×2+8
p(2)=1616+1210+8
p(2)=10.

Hence, the remainder when p(x) is divided by (x2) is 10.

In Exercise 2C RS Aggarwal Class 9, the fifteenth question is a word problem and its comprehensive solution is given below.

15. If p(x)=x35x2+4x3 and g(x)=(x2) show that p(x) is not a multiple of g(x).

We have,
p(x)=x35x2+4x3
g(x)=(x2)

We know that p(x) is a multiple of g(x) if the remainder obtained is zero when p(x) is divided by g(x).

 g(x)=0
(x2)=0
x=2

According to remainder theorem, when p(x) is divided by g(x), the remainder is p(2).

 p(2)=235×22+4×23
p(2)=820+83
p(2)=1623
p(2)=7

∵ The remainder is not equal to zero, the given polynomial p(x) is not a multiple of g(x).

In Exercise 2C RS Aggarwal Class 9, the sixteenth question is about the application of factor theorem.

16. If p(x)=2x311x24x+5 and g(x)= (2x+1), show that g(x) is not a factor of p(x).

We have
p(x)=2x311x24x+5
g(x)= (2x+1)
Here, g(x)=0
2x+1=0
x=12.

For g(x) to be a factor of p(x), the remainder obtained when p(x) is divided by g(x) must be zero.

Putting x=12 in p(x), we get.

p(-12)=2(-12)311(-12)24×(-12)+5
p(-12)=2×1811×144×12+5
p(-12)=14114+2+5
p(-12)=14114+7
p(-12)=111+284
p(-12)=164
p(-12)=4

 p(-12)0, g(x)=2x+1 is not a factor of p(x).

Hence, proved!