1 – 2ab – (a2 + b2) =?

1 – 2ab – (a2 + b2) = 1 – 2ab – a2 – b2= 1 – (2ab + a2 + b2)= 1 – (a + b)2= (1 – a – b)(1 + a + b) a2 – b2 = (a – b)(a + b)

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