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## Homework Statement

A pipe comes diagonally down the south wall of a building, making an angle for 45 degrees with the horizontal. Coming into a corner, the pipe turns and continues diagonally down a west facing wall, still making an angle of 45 degrees with the horizontal. What is the angle between the south wall and west wall sections of the pipe?

## Homework Equations

Dot products invariance under the rotation of a coordinate system

## The Attempt at a Solution

My main problem is actually visualizing the question. I feel as if it just an application of the parallelogram rule for addition of vectors and then finding the angle. Arfken says the solution is 120 degrees.