Length of the diagonal?

Question

The doorway of a family room measures 78 inches by 36 inches. What is the length of the diagonal?

 

I have to show work, please explain.

 

The length of the diagonal is __

Answer 1

If you draw yourself a picture, you'll see that the diagonal forms two right triangles in the doorway.  The diagonal is the hypotenuse, and the length and width of the door are the legs. Use the Pythagorean Theorem to find the length of the diagonal.

 

a² + b² = c²

 

where a and b are the legs and c is the hypotenuse (diagonal).