tan x = sin x / cos x, csc x = 1/sin x, 1/cos x = sec xtanx=sinxcosx,cscx=1sinx,1cosx=secx
tan^2x * csc^2 x = (color(brown)cancel(sin^2 x) / (cos^2 x)) * (1/
(color(brown)cancel(sin^2 x)))tan2x⋅csc2x=(sin2xcos2x)⋅(1sin2x)
=> 1/ cos ^2 x = sec ^2 x = 1 + tan ^2 x