Find the angle between the planes `3x+y+2z=1` and `2x-y+z+3 = 0`.

Explanation

To find the angle between the planes given by the equations \(3x + y + 2z = 1\) and \(2x - y + z + 3 = 0\), we will follow these steps:

### Step 1: Identify the normal vectors of the planes
The normal vector of a plane given by the equation \(Ax + By + Cz + D = 0\) is \(\vec{n} = (A, B, C)\).

For the first plane \(3x + y + 2z = 1\), we can rewrite it in the standard form:
\[
3x + y + 2z - 1 = 0
...