Question

I'm supposed to find the length of x but don't know how

Answer 1

By definition:

$\cos (angle)=\frac{\text{adjacent side}}{Hypotenuse}$

From the picture:

$\begin{gathered} \cos (60)=\frac{x}{20} \\ \frac{1}{2}=\frac{x}{20} \\ \frac{1}{2}\cdot20=x \\ 10=x \end{gathered}$