# Math Help - Functions..

1. ## Functions..

Hi.
I'm having trouble with the following:

If f(x)=|2x+1| and g(x)=x-4, find f(g(1)) and g(f(1))

and

Find the equation of the linear function f if f(1)=-1 and f(4)=8

Thank you for looking it over,any help is greatly appreciated..

2. Originally Posted by Ai Ekio
Hi.
I'm having trouble with the following:

If f(x)=|2x+1| and g(x)=x-4, find f(g(1)) and g(f(1))

and

Find the equation of the linear function f if f(1)=-1 and f(4)=8

Thank you for looking it over,any help is greatly appreciated..
$f(g(x))=|2(x-4)+1|$. Now evaluate at $x=1$.

The other composite is similar.

Oh. I just notice the second half of the problem. To find an equation to a line given 2 points in the plane, simply make use of the point-slope form of a line,

$(y_2-y_1)=m(x_2-x_1)$

where - in your case - $m=\frac{-1-8}{1-4}$

3. Thank you. =)