Question

If f(x) = x² - 7x + k and f(k) = -9, then the value of f(-1) is

(A) -9
(B) -3
(C) 3
(D) 11​

Answer 1

D.) 11

Explanation:

-9=-k^2-7k+k Plugging in k for x

-9=k^2-6k Combine like terms

0=k^2-6k+9 Add 9 to both sides

0=(k-3)(k-3) Factor

k=3

The equation is now

f(x)=x^2-7x+3

so

f(-1)=(-1)^2-7(-1)+3

f(-1)=1+7+3

f(-1)=11