sin(x) = ⁴/₅
sin⁻¹[sin(x)] = sin⁻¹(⁴/₅)
x ≈ 53.13
cos(90 - x) = cos(90)cos(x) + sin(90)sin(x)
cos(90 - 53.13) = cos(90)cos(53.13) + sin(90)sin(53.13)
cos(36.87) = 0cos(53.13) + sin(53.13)
cos(36.87) = sin(53.13)
cos(36.87) = cos(90 - 53.13)
cos(36.87) = cos(36.87)
