posted by GIGI .
veify that each equation is an identity
Does cos2x mean cosine squared? cos^2(x)
If so, then you have
cos^2(x) + sin^2(x)/cos^2(x) * cos^2(x)
= cos^2(x) + sin^2(x)
If you mean cos(2x) then the equation is not an identity (e.g.: x = pi/2)