Step-by-step explanation:

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Step-by-step explanation:

a2 + b2 -c2 - d2 +2ab - 2cd

= (a2 +b2 + 2ab) - ( c2 + d2 + 2cd)

= (a +b)2 -(c - d)2

= [(a + b) - (c + d)] [(a + b) + (c +d)]

( therefore) a2 - b2 = (a + b) (a - b)

= (a + b - c - d) (a + b + c + d). {ans.}