Theorem 1 : For any real numbers x and y , sin x = sin y implies x = nπ + (– 1 ) n y , where n ∈ Z
Theorem 2 : For any real numbers x and y , cos x = cos y , implies x = 2nπ ± y , where n ∈ Z
Theorem 3 : If x and y are not odd mulitple of π / 2 , then tan x = tan y implies x = nπ + y , where n ∈ Z
Numerical : Find the principal & general solutions of the equation sin x = ½