Question

Let $f\left(x\right)=x^3-12x^2+ax+b$ is an increasing function and $f\left(3\right)=3,f\left(4\right)=4$ the

• A. $a=48$
• B. $b=-38$
• C. $a=-48$
• D. $b=38$

Answer 1

The correct option is A $a=48$

Given $f\left(x\right)=x^3-12x^2+ax+b$.

Also given,

$f\left(3\right)=3$

or, $27-108+3a+b=3$

or, $3a+b=84$.......(1).

Also $f\left(4\right)=4$

or, $64-192+4a+b=4$

or, $4a+b=132$......(2).

Now, subtracting (1) from (2) we get,

$a=48$.

Putting the value of $a$ in (1) we get,

$b=-60$.