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CBSE Class 9 Answered

Find the values of a and b so that (x + 1) and (x - 2) are factors of (x3 + ax2 + 2x + b).
Asked by Topperlearning User | 04 Jun, 2014, 01:23: PM
answered-by-expert Expert Answer

If (x + 1) is a factor of x3 + ax2 + 2x + b then

(-1)3 + a(-1)2 + 2(-1) + b = 0

-1 + a - 2 + b = 0

a + b = 3 ...(1)

If (x - 2) is a factor of x3 + ax2 + 2x+ b then

(2)3 + a(2)2 + 2(2) + b = 0

4a + b = -12 ...(2)

Subtracting (1) from (2), we get

3a = -15

Or, a = -5

Using in (1), we get

-5 + b = 3

Or, b = 8

Hence, a = -5, b = 8.

Answered by | 04 Jun, 2014, 03:23: PM
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