Question

Let f(x) = x - 2 and g(x) = x2 - 7x - 9. Find f(g(-1)).

Select one:
a. -21
b. -3
c. 3
d. 21

Answer 1

Plug in -1 for all instances of x in g(x)
Then take that value and plug it in for all instances of x in f(x).

Answer 2

so -2*2-7*-2-9?

Answer 3

\(g(x)=x^2-7x-9\)

\(g(-1)=(-1)^2-7(-1)-9=~?\)

Answer 4

18?

Answer 5

Nope, you should get -1.

Answer 6

how is that?

Answer 7

\((-1)^2=1\)
\(-7(-1)=-(-7)=7\)

\(1+7-9=8-9=-1\)

Answer 8

ok then i take f(-1)=-1-2?

Answer 9

Yep!

Answer 10

=3?

Answer 11

should be -3

Answer 12

but then you multiply it by -1 and it makes it a positive right

Answer 13

x-2
x = -1
-1-2=-3

Answer 14

but what about the f(-1)

Answer 15

f(-1) means that you just replace all instances of x with -1 in the function.

Answer 16

oh ok

Answer 17

Good job!