Question

`vecP+vecQ+vecR=0` and `|vecP|=3, |vecQ|=4, |vecR|=5` then angle between `vecP` and `vecR` is?

Answer 1

These vectors amount to a triangle and their respective magnitudes are a Pythagorean triple .

`:. angle PR = arctan(4/3) = arccos (3/5) = arcsin(4/5)`