The diagonal of a television screen measures 15 inches, and the height measures 9 inches. How wide is the screen?

The first step is to take the lengths, and substitute them into the Pythagorean Theorem: a^2+b^2=c^2

15^2=9^2+b^2

225 = 81 + b^2

subtract 81:

b^2 = 144

take the square root:

b = 12. The width is 12 inches