How do you know cos(-3pi/4) = cos(5pi/4)

Question

asked May 9, 2023 146k views

1 Answer

Codable · Answer 1 · 2023-05-13T03:07:37+0000

We have

$\cos (-(3\pi)/(4))=-\frac{\sqrt[]{2}}{2}$

in this case -3pi/4 and 5pi/4 are coterminal angles

$-(3\pi)/(4)+2\pi=(5\pi)/(4)$

therefore because they are coterminal angles the value of the cosine will be the same

$\cos ((5\pi)/(4))=-\frac{\sqrt[]{2}}{2}$

ANSWER

because they are coterminal angles the value of the cosine will be the same