Question

Find the value of $b$, if $f\left(x\right)=a{x}^2+bx+c,f(-1)=-18$, and $f\left(1\right)=10$.

• A. $-12$
• B. $-4$
• C. $14$
• D. $21$
• E. $28$

Answer 1

Answer: (C)

$14$

Given, $f\left(x\right)=a{x}^2+bx+c,f(-1)=-18,f\left(1\right)=10$
$f(-1)=a-b+c=-18$ and $f\left(1\right)=a+b+c=10$
Now subtract above two equations, we get

$2b=28$

$\Rightarrow b=14$