Find $f[g(x)]$ or $(f \circ g)(x)$
\[
\begin{array}{l}
f(x)=x^{2}+3 x \\
g(x)=x-2
\end{array}
\]
\(\boxed{f[g(x)] = x^2 - x - 2}\)
Step 1 :Let's find the composition of two functions, $f(x)$ and $g(x)$, denoted as $(f \circ g)(x)$ or $f[g(x)]$.
Step 2 :We have $f(x)=x^{2}+3 x$ and $g(x)=x-2$.
Step 3 :To find the composition of two functions, we substitute the second function, $g(x)$, into the first function, $f(x)$.
Step 4 :Substitute $x-2$ (which is $g(x)$) into $f(x) = x^2 + 3x$.
Step 5 :So, $f[g(x)] = (x-2)^2 + 3*(x-2)$
Step 6 :Simplify the expression to get $f[g(x)] = x^2 - x - 2$.
Step 7 :\(\boxed{f[g(x)] = x^2 - x - 2}\)