Solution
Explanation:
Apply the reference angle by finding the angle with equivalent trig values in the first quadrant. Make the expression negative because cosine is negative in the second quadrant.
[tex]cos\frac{-3\pi}{4}[/tex]
Use the following property
[tex]cos(-x)=-cosx[/tex][tex]\begin{gathered} cos(-\frac{3\pi}{4})=-cos\frac{3\pi}{4} \\ =-\frac{\sqrt{2}}{2} \end{gathered}[/tex]
Therefore the value of cosine in the second quadrant is negative
Then, cos (-3π/4) =
[tex]-\frac{\sqrt{2}}{2}[/tex]
