## Trigonometry (10th Edition)

$\cos$ 40$^{\circ}$ = 2 $cos$ 20$^{\circ}$ $\cos$ 40$^{\circ}$ $\approx$ 0.76604444 $\cos$ 20$^{\circ}$ $\approx$ 0.93969262 2 $\cos$ 20$^{\circ}$ $\approx$ 1.87938524 Therefore: $\cos$ 40$^{\circ}$ $\ne$ 2 $cos$ 20$^{\circ}$