Question

If Cos(t)=-7/8 with `pi<=t<=3pi/2`, how do you find the value of cos(2t)?

Answer 1

`17/32`

Explanation:

Apply the trig identity: cos 2a = 2cos^2 a - 1
`cos 2a = 2(49/64) - 1 = 49/32 - 1 = 17/32`