# The angle between two planes

**Question**

Find the angle between them the two planes below.

- Plane 1 = r.(i + 3j – 2) = 1
- Plane 2 = r.(2i + j – 3k) = 9

**Answer**

- 38.21

*Notes:*

*cos z = (Unit vector of z1)*(Unit vector of z2)*

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