If you separate the variables, you have { sin(2x)/cos2x }dx = (3/y)dy
Using trig substitutions, we have (2/3)tanx dx = dy/y
This should be no problem from here, as -(2/3)ln(cosx) = ln(y) + ln(constant) = ln(cy)
Then, just simplify the expression (cosx) = (cy)(-3/2)
(Note: Absolue value symbols left off of ln functions!)