[tex]\bf (\stackrel{\stackrel{adjacent}{x}}{-20}~,~\stackrel{\stackrel{opposite}{y}}{-21})\impliedby \textit{let's find the \underline{hypotenuse}}
\\\\\\
\textit{using the pythagorean theorem}
\\\\
c^2=a^2+b^2\implies c=\sqrt{a^2+b^2}
\qquad
\begin{cases}
c=hypotenuse\\
a=adjacent\\
b=opposite\\
\end{cases}
\\\\\\
c=\sqrt{(-20)^2+(-21)^2}\implies c=\sqrt{841}\implies c=29
\\\\\\
cos(\theta )=\cfrac{\stackrel{adjacent}{-20}}{\stackrel{hypotenuse}{29}}[/tex]
