Robert J. answered 04/04/13
Certified High School AP Calculus and Physics Teacher
This problem can be solved in a much simpler way.
sin(-2x) = cos(3x)
=> cos(pi/2 + 2x) = cos(3x)
pi/2 + 2x = 3x => x = 0.5pi
or
pi/2 + 2x = -3x + 2k*pi
k = 1, x = 0.3pi
k = 2, x = 0.7pi
k = 3, x = 1.1pi
k = 4, x = 1.5pi
k = 5, x = 1.9pi