Question

put - b in place of b in identity I) do you get identity II) ?

Answer 1

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Answer 2

(a+b)^2=a^2 +2ab+b^2
put b = -b
(a-b)^2= a^2 +2a(-b)+ (-b)^2
(a-b)^2 =a^2-2ab+b^2
this is verified