This is the last tip using geometrical shapes, and it really gives it away! We start again with a right triangle:

We use four copies to form a large square that happens to form an inside square (colored in yellow):

Now, here is another arrangement of the same four triangles. As you can see, in this case, they form two rectangles. The two corner areas in the lower left and upper right are colored to be able to distinguish them easily. Here is the second shape:

Compare the last two figures. Are they the same size?  Calculate their areas and write them down to check if they are the same or not. If their areas are equal, then the following geometrical equation should be correct:

=

As a final step, you know that if either side of the equal sign are truly equal or balanced, you can add or subtract the same amount on both sides and still maintain the equality. So let's remove the four triangles from each side to get the following equation:

=

Does that give it away or what? Check out your theory:

Remember that you can use the template included.

If you didn't get it, don't worry, the next and last tip really gives it away. So go right ahead...