Lesson 3 of 8
The Pythagorean Theorem
This one is a star player. It works only on right triangles (a triangle with a 90 degree angle). It links the three sides together.
FORMULA
a^2 + b^2 = c^2, where a and b are the two legs (the short sides) and c is the hypotenuse (the longest side, across from the right angle).
When to use it
Use it whenever you have a right triangle and you know two sides and need the third. The hypotenuse c is always the side opposite the right angle, and it is always the longest.
- 1Find the right angle and label the hypotenuse c.
- 2Plug the two known sides into a^2 + b^2 = c^2.
- 3Square the numbers, then solve for the missing side.
- 4Take the square root at the end to get the side length.
Example: legs of 3 and 4. Then 3^2 + 4^2 = 9 + 16 = 25, and c = square root of 25 = 5. So the hypotenuse is 5.