# Calculating angle between two vectors

1. Sep 10, 2010

### jpd5184

1. The problem statement, all variables and given/known data

Use the definition of scalar product, a·b = ab cos θ, and the fact that a·b = axbx + ayby + azbz to calculate the angle between the two vectors given by a = 1.0 ihat + 5.0 jhat + 1.0 khat and b = 6.0 ihat + 3.0 jhat + 4.0 khat.

2. Relevant equations

a·b = ab cos θ

3. The attempt at a solution

i really dont have any clue were to start

2. Sep 10, 2010

### Andrew Mason

Write out the expression for $\theta$ in terms of the length of a x length of b and $a_xb_x + a_yb_y + a_zb_z$ (hint: you need the arccos function and pythagoras' theorem).

AM