# Homework Help: Angle between two vectors

1. Feb 2, 2012

### Uira

Hello, Ive been trying to solve this problem for hours now, but i keep getting it wrong. Been looking for examples but i dont seem to find one with a good explanation, so any help is appreciated.

The problem:

Consider two displacements, one of magnitude 2.6 and another of magnitude 3.9. What angle between the directions of these two displacements give a resultant displacement of magnitude a) 5.7m b)2.6m c)3.2

2. Feb 2, 2012

### Staff: Mentor

This is referring to addition of the displacements.

You have a triangle, and know the lengths of the 3 sides. Find the angle/s.

3. Feb 2, 2012

### HallsofIvy

A formula that will help is the cosine law. If a triangle has sides a, b, and c and C is the angle opposite side c, then $c^2= a^2+ b^2- 2ab cos(C)$