# If f(x) = x^2 + 3x and g(x) = 4x - 1, what is (f@g)(x)?

In this example $g \left(x\right)$ becomes the input for $f \left(x\right)$. After all of the substitutions are made foil ${\left(4 x - 1\right)}^{2}$, distribute $3 \left(4 x - 1\right)$ and then combine the like terms.
$\left(f \circ g\right) \left(x\right)$
$f \left(g \left(x\right)\right)$
$f \left(4 x - 1\right) = {\left(4 x - 1\right)}^{2} + 3 \left(4 x - 1\right) = 16 {x}^{2} - 8 x + 1 + 12 x - 3 = 16 {x}^{2} + 4 x - 2$