Chapter 2 - Acute Angles and Right Triangles - Section 2.2 Trigonometric Functions of Non-Acute Angles - 2.2 Exercises - Page 59: 45

$\sin$$^{2}$ 120$^{\circ}$ + $\cos$$^{2}$ 120$^{\circ}$ = 1

$\sin$$^{2}$ 120$^{\circ}$ + $\cos$$^{2}$ 120$^{\circ}$ $\sin$$^{2}$ 120$^{\circ}$ = $\frac{\sqrt3}{2}$ $\cos$$^{2}$ 120$^{\circ}$ = -$\frac{1}{2}$ Therefore: = ($\frac{\sqrt3}{2}$)$^{2}$ + ($\frac{1}{2}$)$^{2}$ = ($\frac{3}{4}$) + ($\frac{1}{4}$) = 1 $\sin$$^{2}$ 120$^{\circ}$ + $\cos$$^{2}$ 120$^{\circ}$ = 1