There are several different equations that can be used to find missing sides, these can be trigonometric functions or the distance formula. The trigonometric functions consist of sine (opposite/hypotenuse), cosine (adjacent/hypotenuse), and tangent (opposite/adjacent. The adjacent side is represented by the side next to the given angle measure, the opposite is the side that is connected to adjacent side and across from the given angle, and the hypotenuse is the diagonal that connects the opposite side to the given angle- most notable because its line isn't straight like the other sides.
The distance formula is used to find the measurement of missing side lengths in all quadrilaterals, and it's: D = sqrt(x2 - x1)^2 + (y2 - y1)^2 where x are the x-coordinates of two given points and y are the y-coordinates of the same two given points.
