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Media > TDT > Reasoning > R_A_D_AS1_S1_fig1

R_A_D_AS1_S1_fig1

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Each of the triangular numbers 6 and 10 is modelled with rows of squares. Then one shape is rotated 180 degrees so that the two triangular numbers fit together, creating a 4 by 4 square.

Proof by modelling.

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