add section angle between vectors

uni/mmme/1026_maths_for_engineering/vectors.md

@@ -187,6 +187,13 @@ which has a magnitude and direction given by the line $\overrightarrow{OP}$.
 
 A point $(x, y, z)$ in Cartesian space has the position vector $r = x\pmb i + y\pmb j + z\pmb k$.
 
+## Angle Between Vectors
+
+By rearranging the [dot product equation](#the-scalar-product-inner-product-dot-product) you can get
+an equation to find the angle, $\theta$, between two vectors:
+
+$$\cos\theta = \frac{\pmb a \cdot \pmb b}{|\pmb a||\pmb b|} = \frac{a_1b_1 + a_2b_2 + a_3b_3}{|\pmb a ||\pmb b|}$$
+
 # Applications of Vectors
 
 ## Application of Vectors to Geometry