Identify where the 90 degree angle is located on the triangle. This will help you label the sides correctly. All right triangles have exactly one 90 degree angle.
Label the hypotenuse with a "C." The hypotenuse is located directly opposite of the 90 degree angle. It is also the longest side.
Label the remaining sides of the triangle as "A" and "B." Do not worry about which side is which, labeling only matters for the hypotenuse.
Highlight which opposite side you must find on the triangle.
Substitute the known side length measurements into the Pythagorean theorem formula. Leave the unknown measurement as a variable. The formula is "A" squared plus "B" squared equals "C" squared. The Pythagorean theorem can be used to find any missing side of a right triangle.
Make sure you square each side length's measurement. Leave the square symbol on the missing variable intact for now.
Solve the equation to find the length of the unknown opposite side. You can do this by isolating its variable on one side of the equal sign and placing all actual numbers on the opposite side. Make sure you perform all the necessary addition and subtraction so you are left with only one variable and one number.
If you are solving for the hypotenuse, the missing variable and known side measurements will already be properly placed on either side of the equation. You will only need to add sides "A" and "B" together.
However, if you are solving for "A" or "B," you will be required to perform some basic algebra to isolate the variable.
Make sure you take the square-root of each side of the equation to remove the "square" symbol off your opposite side's variable.
Verify you have the right answer by using a calculator. If your answer is different, try retracing your steps and checking your math.