Answer
The equivalent trigonometric form is $8(cos 120^\circ + i sin120^\circ)$.
Work Step by Step
$- 4 + 4i\sqrt{3}$ is at $120^\circ$ with absolute value $\sqrt{(-4)^2 + (4\sqrt{3})^2} = 8$, the equivalent trigonometric form is $8(cos 120^\circ + i sin120^\circ)$.