For (a + b)(a – b), remove corner square b² from square a²; rearrange the remaining L-shape into rectangle (a + b) by (a – b). For (a + b + c)², divide a square into 9 blocks yielding a² + b² + c² + 2ab + 2bc + 2ca.
Identities in algebra can sometimes be shown as area relationships. The figure shown corresponds to the identity (a + b)² = a² + 2ab + b². Do you see how? Draw figures corresponding to the identities (a + b)(a – b) = a² – b² and (a + b + c)² = a² + b² + c² + 2ab + 2bc + 2ca.
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