You can only use Pyhagorean Theorem when there is a right angle. You use it when a side lenght is unknown, but two other sides are known. If you are finding c, do the equation a^2+b^2=c^2. If you are finding b, do the equation b^2=c^2-a^2. If you are trying to find a, do the equation a^2=c^2-b^2. Hope this helped
