Question

Given f, of, x, equals, minus, 4, x, squared, minus, 4, x, plus, 18f(x)=−4x
2
−4x+18, find f, of, 9f(9)

Answer 1

To find \( f(9) \) for the function \( f(x) = -4x^2 - 4x + 18 \), we can substitute \( x = 9 \) into the function.

\[
f(9) = -4(9)^2 - 4(9) + 18
\]

Now, calculate \( 9^2 \):

\[
9^2 = 81
\]

Now, substitute this back into the function:

\[
f(9) = -4(81) - 4(9) + 18
\]

Now calculate \( -4(81) \):

\[
-4(81) = -324
\]

Calculate \( -4(9) \):

\[
-4(9) = -36
\]

Now, combine everything:

\[
f(9) = -324 - 36 + 18
\]
\[
f(9) = -324 - 36 + 18 = -342
\]

Thus, the final value is:

\[
f(9) = -342
\]