3a(2a+7)-(2a+1)(3a-4)
3m(1-6m)-(2m-1)(2m+1)
5(a-b)+(a+b)(a-b)-a^2

3a(2a+7)-(2a+1)(3a-4)=6а^2 +21а-6а^2 +8а-3а+4=26а+43m(1-6m)-(2m-1)(2m+1)=3m-18m^2 - 4m^2 - 2m+2m+1=-22m^2 +3m+15(a-b)+(a+b)(a-b)-a^2=5a-5b+a^2 - b^2 - a^2 =5a-5b-b^2

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