Question

cos2x < cosx

Answer 1

try using cos2x = 2 cos^2 x -1

Answer 2

This will result in Quadratic in cos x.
Then sove for the roots

Answer 3

thank you!

Answer 4

these are worth remembering!! Have "fun"!!!


sin(α + β) = sin(α)cos(β) + cos(α)sin(β)
sin(α – β) = sin(α)cos(β) – cos(α)sin(β)
cos(α + β) = cos(α)cos(β) – sin(α)sin(β)
cos(α – β) = cos(α)cos(β) + sin(α)sin(β)