Question
In the following cases, determine whether the given planes are parallel or perpendicular, and in case they are neither, find the angles between them:
2x – y + 3z – 1 = 0 and 2x – y + 3z + 3 = 0
Solution
The given planes are
2x – + 3z – 1 = 0 ...(1)
and 2x – y + 3z + 3 = 0 ...(2)
Direction ratios of normal to plane (1) are 2, –1, 3.
Direction ratios of normal to plane (2) are 2, – 1, 3.
Now, 
∴ given planes (1) and (2) are parallel.
