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(a+b)²-(a-b)²=
=(a+b-(a-b))*(a+b+a-b)=
=(a+b-a+b)*2a=
=2b*2a=
=4ab
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(x+3)*(x-2)-3(x-4)=
=x²-2x+3x-6-3x+12=
=x²-2x+6
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