DefinitionWhen expressing a function in sine and cosine, you write the function in terms of sine and cosine, using trigonometric identities to simplify/manipulate expressions. This would include learning the Pythagorean identity, sum and difference identities, double-angle identities, and half-angle identities that are all essential for this to come easier and more naturally. Writing functions as sine and cosine is helpful in solving trigonometric equations, determining important integrals, and studying repetitive behavior in nature. For instance, tan(x)→ is tan(x)=sin(x)cos(x) by definition of the tangent as the sine over the cosine.
