Question

if f(x) = cos2x, find f(3pi/4).

Answer 1

try to use these three trigo identities related to cos(2x)

1. \[\cos ^{2}(x)-\sin ^{2}(x)\]
2. \[2\cos ^{2}(x)-1\]
3. \[1-2\sin ^{2}(x)\]

place \[x= (3\pi/4)\] and you will get the same answer for all three of the equation.

Answer 2

yeah, n remember to set your calculator to radian mode.

Answer 3

thank you. :)