The rectangular component of force F shown in Fig 2-15a are found using the parallelogram law,so that F = F + F Because these component form a right triangle,their magnitudes can be determined form
Instead of using the angle theta, however, the direction of F can also be defined using a small "slope" triangle, such as shown in Fig 2-15b. Since this triangle and the larger shaded triangle are similar, the proportional length of the sides gives