Soluion:
[tex]\cos(-180^o)[/tex]Apply the reference angle by finding the agle with equivalent trig onometry values in the first quadrant. The expression woud be negative because the angle i in the second quarany at and cosine is negative in the second quadrant.
[tex]\begin{gathered} \cos(-180^o)=-\cos(0) \\ \\ \cos(180^o)=-1 \end{gathered}[/tex]ANSWER: -1
