Methods 1 angle doubling formula+inductive formula: denominator = [2 sin (π/4-a/2) sin (π/4+a/2)] = sin 2 (π/4-a/2) = sin (π/2-a) = COSA; Original formula = sina/cosa =tana method 2 and differential angle formula+double angle formula denominator = [2sin (π/4-a/2) sin (π/4+a/2)] = 2 (sinπ/4cosa/2-cosπ/4cina/2) (sinπ/4cosa = Original formula = sina/cosa =tana Method 3 and differential product because cos [(π/4-a/2)+(π/4+a/2)] = 0 = = cos (π/4-a/2) cos (π/4+a/2)-sin (π/). 4+A/2)] = COSA = = COS (π/4-A/2) COS (π/4+A/2)+SIN (π/4-A/2) SIN (π/4+A/2) Subtract the above two expressions: COSA = 2 SIN (π/2).