The resultant of two forces acting on a body has a magnitude of 80 pounds. the angles between the resultant and the forces are 20á and 52á. find the magnitude of the larger force.

The basic idea is that you form a parallelogram with those two vectors as the two different side lengths another way to see it: start at the tip of one vector and move in the same direction as the other vector (and the same length as the other vector)

With any parallelogram, the adjacent angles are supplementary

180-52-20= 108 degrees