# Are the planes #x+y+z=1# , #x-y+z=1# parallel, perpendicular, or neither? If neither, what is the angle between them?

##### 1 Answer

#### Explanation:

We can find the angle between two planes, by finding the angle between the normals to the plane:

When given the equation of a plane in Cartesian form:

The normal vector to the plane is:

Let:

Then:

We can find the angle between these normals using the Dot Product:

**2 d.p.**

If the planes were perpendicular, the the angle between them would be

If the planes were parallel, the the angle between them would be

Plot: