计算题：(a-b+c)(b-a+c)= （2a-b-c）^2= (a-3)(a^2+9)(a+3)=

(a-b+c)(b-a+c)=[c+(a-b)][c-(a-b)]=c^2-(a-b)^2=c^2-(a^2-2ab+b^2)=c^2-a^2+2ab-b^2（2a-b-c）^2=(2a)^2+b^2+c^2-2*2a*b-2*2a*c+2bc=4a^2+b^2+c^2-4ab-4ac+2bc(a-3)(a^2+9)(a+3)=(a-3)(a+3)(a^2+9)=(a^2-9)(a^2+9)=...在帮我解两个好吗？（7x-y）（-7x+y）=(-3m-n)(3m+2n)=谢谢~（7x-y）（-7x+y）=-(7x-y)(7x-y)=-(7x-y)^2=-(49x^2-14xy+y^2)=-49x^2+14xy-y^2(-3m-n)(3m+2n)=-(3m+n)(3m+2n)=-(3m+2n)^2=-(9m^2+12mn+4n^2)=-9m^2-12mn-4n^2提示：运用完全平方公式