A square + B square = ?

{(A + B)}^{2} = (A + B) (A + B) \Rightarrow {(A + B)}^{2} = A (A + B) + B (A + B) \Rightarrow {(A + B)}^{2} = A^{2} + AB + AB + B^{2} \Rightarrow {(A + B)}^{2} = A^{2} + B^{2} + 2 AB \Rightarrow A^{2} + B^{2} = {(A + B)}^{2} - 2 AB

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