f(x) = If[0 < x ≤ (2 * π), sin(x)]
g(x) = If[0 < x ≤ (2 * π), cos(x)]
A = Intersect(f(x), g(x), (0.7853981677626303, 0.7071067842731973))
B, C = Intersect(f(x), g(x), 0, (2 * π))
Pindala = IntegralBetween(f(x), g(x), 0.79, 3.93)