If (x + 2) is a factor of p (x) = ax3 + bx2 + x – 6 and p(x) when divided by (x – 2) leaves a remainder 4, prove that a = 0 and b = 2.

We have,

p (x) = ax3 + bx2 + x – 6


It is given in the question that, (x + 1) is a factor of p (x)


x + 2 = 0


x = - 2


f (-2) = 0


a (-2)3 + b (-2)2 + (-2) – 6 = 0


- 8a + 4b – 2 – 6 = 0


- 8a + 4b – 8 = 0


- 4 (2a – b + 2) = 0


2a – b + 2 = 0 (i)


Also, it is given in the question that when p (x) is divided by (x – 2) then it leaves a remainder 4


p (2) = 4


a (2)3 + b (2)2 + (2) – 6 = 4


8a + 4b + 2 – 6 = 4


8a + 4b – 4 - 4= 0


4 (2a + b – 2) = 0


2a + b – 2 = 0 (ii)


Now, adding (i) and (ii) we get:


2a – b + 2 + 2a + b – 2 = 0


4a = 0


a = 0


Putting the value of a in (ii), we get:


2 (0) + b – 2 = 0


b – 2 = 0


b = 2


Hence, it is proved that the value of a is 0 and that of b is 2


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