**Q: What is the (straight-line) distance between points A and B on the figure below?**

Answer: 7

Explanation: We are finding the length of the green segment below:

This requires the three-dimensional version of the distance formula:

There is another way to do this, using a progression of two right triangles, with the green segment being the hypotenuse of the second triangle, but I find the above formula much simpler. It is just an extension of the ‘usual’ (2-dimensional) distance formula we are so familiar with from Algebra and Geometry.

BUT if you want an even *easier* way, and I know you do, use my TI-84 Plus program ‘DIST3D’.