Hey, it's me again. I was looking at the picture and an idea fell out of the sky.
I don't know how to draw on this site, so I'll try to explain it in words.
You have the large square which is the outside one.
You have the small square which is the inside one.
Draw a line from point A to point C and
draw a line from point D to point B.
Now you have four tiny squares, each of which is cut into two equal triangles by a diagonal line.
The small square contains four of those triangles and
the large square contains eight of those triangles.
Thus, the large square contains twice the area of the small square.
The area of the small square is 60, so twice that is the area of the large square, i.e., 120
Neat, huh? Even if I do say so myself. TTFN.
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