诺梵
幼苗
共回答了18个问题采纳率:88.9% 举报
考虑这几个公式
a^2 - b^2 = (a+b)*(a-b)
a^2+2ab+b^2 = (a+b)^2
a^2-2ab+b^2 = (a-b)^2
于是
1.(1) (16 + 7/13 + 1/12) * (7/13 - 1/12) = (16+ 97/156) * 71/156 = ...
(2) 200* (47+3/7) = ...
2.(1) 15x*(x-2)*(y+4) = 0
(2) x*(m-2) = 0.4*3.5 = 1.4
(3) 3x-2 = 0 因此就剩下 2x = 4/3
3 (1) 100*46 = 4600
(2) (204+96)^2 = 90000
4 (a+1)^2 + (b-2)^2 = 0 ==> a=-1,b=2
2a²+4b-3 = 2+8-3=7
5 1/2xy*(a-b)^2 = 5/2*6^2 = 90
6 (n-1)*n*(n+1)*(n+2)+1 = (n^2 -1)*[(n+1)^2 - 1] + 1
= [n(n+1)]^2 - n^2-(n+1)^2 + 2
=[n(n+1)]^2 - 2*n^2 - 2n + 1
=[n(n+1)-1]^2 是完全平方
7 a^2b+ab^2 = ab(a+b) = 1*3=3
1年前
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