### Number 204 of a series

Math time again. Some time ago I had the idea to clear out shelf space, so I dumped all the copies of Schaum’s Outline books that are available on Kindle. This is from Schaum’s *Vector Analysis*, Chapter 2.

2.11. Show that the vectors

A= −i+j,B= −i−j– 2k,C= 2j+ 2kform a right triangle.

**i**, **j**, and **k** are the unit vectors parallel to the 3D coordinate axes. To be clear, imagine each vector as a straight line oriented in space but movable. Can you move the three lines into position to form a right triangle? Give a mathematical proof.

The answer is in the book, but you know better than to look for the answer. Post your answer as a comment below.