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