To find the missing side length, one angle measurement and one side length is required to be found. With these numbers they are plugged in either of the trigonometric ratios(sine, cosine, tangent ). FRom here, the missing side is isolated using multiplication property of equality. To find an angle measurement, you need 2 side lengths. These side lengths are plugged into the trigonometric functions as well but the angle measurement is substituted as Θ. Instead of using multiplication to isolate Θ, the inverse of the function (sin-1, tan-1, cos-1) is applied to the ratio(o/h, a/h, o/a). Trigonometric functions are used on both. They both can help find the other.