Let $x = \sec A + \sin A$ and $y = \sec A - \sin A$, simplify $ \left( \dfrac 2{x+y} \right)^2 + \left( \dfrac{x-y}2 \right)^2 $.
x + y = 2sec A
x - y = 2sin A
(2 / (2secA))^2 + (( 2sin A) / 2)^2 =
1 / sec^2A + sin^2 A =
cos^2 A + sin^2 A =
1
