csc = 1/sin
csc^4 -csc^2 = cot^4 *cot^2
cot = cos/sin
1/sin^4 - 1/sin^2 = (cos/sin)^4 *(cos/sin)^2
(1 - sin^2)
-------------- = (cos^4)/(sin^4) *(cos^2)/(sin^2)
sin^4
sin^2 +cos^2 = 1 so from this result 1-sin^2 = cos^2
cos^2 cos^6
---------- = --------- cross multiply
sin^4 sin^6
sin^6 *cos^2 = sin^4 *cos^6 divide both sides by sin^4*cos^2
sin^2 = cos^4
