Move the vertices (corners) of the triangle. Notice that it always stays right-angled.
Step 1: Click the 'Show Lengths' box and see if you can find a connection between the lengths of the right-angled triangle. i.e. if you had 2 of the lengths, would you be able to find the 3rd length? (Move onto step 2 if you're struggling)
Step 2: Click the 'Show Squares' box. This may help you to find a connection between the lengths of the right-angled triangle. (Move onto step 3 if you're struggling)
Step 3: Click the 'Show Areas' box. Can you see the connection now? Can you write it down as an equation?