Answer
$\cos 1800^{\circ}=1$
Work Step by Step
1. What we know about 1800 degree angle
$\theta=0^{\circ}$ (because it is a co-terminal angle and values of x and y will be the same)
$x=1$
$y=0$
$r=1$
2. Substitute in:
$\cos\theta=\frac{x}{r}=\frac{1}{1}=1$
