Find the exact value of cos (2a)

Question

9.99K viewsOctober 30, 2017trigonometry

0

admin 60 October 27, 2017 1 Comment

Find the exact value of $cos (2\alpha ) , where. cos(\alpha ) = -\frac{\sqrt{5}}{4}, \frac{\pi }{2}< \alpha < \pi$

cos or cot?

score 0 · Answer 1 · 2017-10-30T05:38:32+00:00

0

Use the third formula for the double-angle