Question

If $(x+1)$ and $(x-1)$ are factor of $P{x}^3+x^2-2x+9$ then value of P are

• A. 12
  
• B. 10
  
• C. 11
• D. 8

Answer 1

Answer: (A)

12

$x+1=0x=-1x-1=0x=1$

Putting $x=-1$ in given equation we get

$P{x}^3+x^2-2x+9=P(-1{)}^3+(-1{)}^2-2(-1)+9=-P+1+2+9=-P+12\Rightarrow -P=-12\therefore P=12$

Putting $x=1$ is given equation we get

$P{x}^3+x^2-2x+9P(1{)}^3+1^2-2\times 1+9P+1-2+9P-1+9P+8=0\Rightarrow P=-8$

So, $P=(12,-8)$ So value of $P$ is $12$ as negative cannot be accepted.