Texas Instruments
Texas Instruments: Applying the Pythagorean Theorem
students can use the Pythagorean Theorem and distance formula to determine unknown measurements.
BBC
Bbc: Pythagoras' Theorem
You can pick up some valuable pointers on how to apply the Pythagorean Theorem here. When you finish working your way through the pages you can take an on-line "Test Bite," and check your understanding.