y=(1 where t is a constant The basic trigonometric functions sine and cosine cos(x) describe sinusoidal functions which are 90 out of phase The trigonometric identities are used in geometric calculationsy = (1 - 2e-x/t) where t is a constant. Trigonometric Functions The basic trigonometric functions sine and cosine describe sinusoidal functions which are 90o out of phase. The trigonometric identities are used in geometric calculations