Question

If cos²a - sin²a = tan²b then show that cos²b - sin²b = tan² a.

Answer 1

Let a=45°
${ \cos(45) }^{2} - { \sin(45) }^{2} = 0 = { \tan(0) }^{2} \\ \\ { \cos(0) }^{2} - { \sin(0) }^{2} = 1 = { \tan(45) }^{2} \\ \\ z \\ verified$