fix vector formatting issue

uni/mmme/1026_maths_for_engineering/vectors.md

@@ -248,7 +248,7 @@ $$\frac{x-x_0}{d_1} = \frac{y-y_0}{d_2} = \frac{z-z_0}{d_3}$$
 A *plane* can be defined by specifying either:
 
 - three points (as long as they're not in a straight line)
-- a point on the plne and two directions (useful for a parametric form)
+- a point on the plane and two directions (useful for a parametric form)
 - specifying a point on the plane and the normal vector to the plane
 
 #### Specifying a Point and a Normal Vector
@@ -263,7 +263,7 @@ $$(\pmb r - \pmb a) \cdot \pmb n = 0$$
 
 So the *vector equation* of the plane is
 
-$$\pmb r \cdot \pmb n = \pmb a \cdot n = d$$
+$$\pmb r \cdot \pmb n = \pmb a \cdot \pmb n = \pmb d$$
 
 where $\pmb r = (x, y, z)$ and the vectors $\pmb a$ and $\pmb n$ are known.
 
@@ -291,6 +291,7 @@ and so the equation of the plane is
 
 $$(\pmb r - \pmb a)\cdot((\pmb c - \pmb a)\times(\pmb c - \pmb b)) = 0$$
 
+
 #### The Angle Between Two Planes
 
 ... is the same as the angle between their normal vectors