(a-2b+3c)^2-(a+2b-3c)^2
(a-2b+3c)^2-(a+2b-3c)^2 =(a-2b+3c-a-2b+3c)×(a-2b+3c+a+2b-3c) =(-4b+6c)×2a =-8ab+12ac
原式(a-2b+3c)^2-(a+2b-3c)^2 变形为[a-(2b-3c)]^2-[a+(2b-3c)]^2 可以看着(a-b)^2-(a+b)^2=-4ab 原式=-4a*(2b-3c) =-8ab+12ac
(a-2b+3c)^2-(a+2b-3c)^2=[(a-2b+3c)+(a+2b-3c)][(a-2b+3c)-(a+2b-3c)]=2a(-4b+6c)=-8ab+12ac
(a-2B+3c-a-2b+3c)(a-2b+3c+a+2b-3c)=12ac-8ab
温馨提示:a?-b?=(a+b)(a-b)
根据公式(A+B)(A-B)=A^2-B^2当A=a-2b+3c B=a+2b-3c时 (a-2b+3c)^2-(a+2b-3c)^2 =[(a-2b+3c)+(a+2b-3c)][(a-2b+3c)-(a+2b-3c)] =(a-2b+3c+a+2b-3c)(a-2b+3c-a-2b+3c) =2a(-4b+6c) =-8ab+12ac
12ac-8ab
原式=[(a-2b+3c)-(a+2b-3c)][(a-2b+3c)+(a+2b-3c)] =(-4b+3c)(2a) =-8ab+6ac
=(a-(2b-3c))^2-(a+(2b-3c))^2 =a^2-2a(2b-3c)+(2b-3c)^2-a^2-2a(2b-3c)-(2b-3c)^2 =-4a(2b-3c)
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