# Math Help - Solving trigo

1. ## Solving trigo

cos3X=sinX

Find X, 0 degree < x < 360 degree

2. Originally Posted by ose90
cos3X=sinX

Find X, 0 degree < x < 360 degree

There's the hard way and the easy way. Personally I like the easy way best:

From the complementary angle formulae: $\cos (3x) = \sin x \Rightarrow \cos (3x) = \cos (90 - x)$.

Case 1: $3x = 90 - x + 360 n$ where n is an integer.

Solve for x and substitute appropriate values of n to get all values of x satisfying the given domain.

Case 2: $3x = -(90 - x) + 360 n$ where n is an integer.

Solve for x and substitute appropriate values of n to get all values of x satisfying the given domain.

3. Thank you very much!