# Math Help - How to calculate g(f(x))

1. ## How to calculate g(f(x))

I'm having a bit of trouble with this one:

If f(x) = -5x+6 and g(x) = 4x+5, find g(f(x)).

Shouldn't it be -20x+30??

Any help on how to solve this problem would be appreciated.

2. Originally Posted by softwareguy
I'm having a bit of trouble with this one:

If f(x) = -5x+6 and g(x) = 4x+5, find g(f(x)).

Shouldn't it be -20x+30??

Any help on how to solve this problem would be appreciated.
g(f(x)) = g(-5x+6) = 4(-5x+6) +5 = .....

3. g(f(x)) says g(-5x+6) so you plug that into your x for g.

=4(-5x+6)+5

6*4=24 + 5=29

4. The composition says, where ever you see "x" in g(x), to put the function f(x):

$g(x) = 4x+5 \Rightarrow g(f(x)) = 4(-5x+6) + 5 \Rightarrow -20x+24+5 \Rightarrow -20x+29$

5. Originally Posted by Debsta
g(f(x)) = g(-5x+6) = 4(-5x+6) +5 = .....
f(x) = -5x+6
g(x) = 4x+5
g(f(x)) = g(-5x+6)
= 4(-5x+6) + 5
= -20x +24 +5
= -20x + 29