How do you find the unknown side of a right triangle?

Use Pythagoras's equationa^2 + b^2 = c^2

where c is the hypotenuse - the longest side which is opposite the right angle

a and b are the two smaller legs.

So, if the two legs are known and the hypotenuse is unknown:

1. square the two known sides;
2. add the numbers together
3. take the square root.

This is the measure of the hypotenuse.

Suppose the hypotenuse and one side is known, the other is unkown:

1. square the two known sides;
2. subtract the smaller answer from the larger;
3. take the square root.

This is the measure of the missing leg.