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观察下列各式的计算过程:5×5=0×1×100+25,15×15=1×2×100+25,25×25=...

∵5×5=0×1×100+25,15×15=1×2×100+25,25×25=2×3×100+25,

[10(n-1)+5]×[10(n-1)+5]=100n(n-1)+25.

5(2n—1)^2=(n—1)*n*100+25

5n×5n=(n-1)×n×100+25

(1)95 2 =9×10×100+25=9025; (2)①115 2 =11×12×100+25

∵15×15=1×2×100+25=225,25×25=2×3×100+25=625,35×35=3

15x15=(10+5)(10+5) =10x10十10x5+5x10+5x5 =1010+2x

45×45=4×5×100+25=2025 个位数是5的两个两位数相乘,所得的积等于

(10n+1)^2=n*(n+1)*100+5^2

(1)15 2 =1×(1+1)+25=225,25 2 =2×(2+1)×100+25=625,3

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