tanx + ctgx -2csc2x = 0
tanx = sinx/cosx , ctgx = cosx/sinx , csc2x = 1/sin2x, and sin2x = 2sinxcosx
sinx/cos/ + cosx/sinx - 2/sin2x = o
( sinx/cosx + cosx/sinx - 2/2sinxcosx = 0 )* sinxcosx
sin^2x + cos^2x -1 = 0 , sin^2x + cos^2x = 1
1 - 1 = 0
0 = 0