# How do you factor by grouping 3x^3 + 15x^2 - 4x - 20?

Collect$x$ betwen the first and third term and $5$ between the second and fourth:
$x \left(3 {x}^{2} - 4\right) + 5 \left(3 {x}^{2} - 4\right) =$
$= \left(3 {x}^{2} - 4\right) \left(x + 5\right)$