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Triangles Within Squares
Age 14 to 16
Challenge Level 
There is a very strong connection between this problem and the "Sequences and Series" problem.
Can you see the rectangles made from two triangular numbers in the square?
Can you explain why there is always one left over?
Can you see the rectangles made from two triangular numbers in the square?
Can you explain why there is always one left over?
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