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1/5乘6乘7+1/6乘7乘8+1/7乘8乘9+1/8乘9乘10+1/720

1/(5×6×7)+1/(6×7×8)+1/(7×8×9)+1/(7×8×9)+1/720 =[1/(5×6)-1/(6×7)]/2+[1/(6×7)-1/(7×8)]/2+[1/(7×8-1/(8×9)]/2+1/720+1/720 =[1/(5×6)-1/(8×9)]/2+1/360 =1/15-1/36 +1/360 =7/180+1/360 =14/360+1/360 =1/24

5×6乘七分之1 +6乘7×8分之1 +7乘8×9分之1 +8乘9×10分之1 =2分之1×[5×6分之1-6×7分之1+6×7分之1-7×8分之1+7×8分之1-8×9分之1+8×9分之1-9×10分之1] =2分之1 ×(5×6分之1-9×10分之1) =2分之1×(30分之1-90分之1) =2分之1×45分之1 =90分之1

5乘6乘7分之1加上6乘7乘8分之1加上7乘8乘9分之1 =1/5*6*7+1/6*7*8+1/7*8*9 =(8*9/5*6+9/6+1)*1/7*8*9 =(12/5+1/2+2)*1/7*8*9 =(29/10+2)*1/7*8*9 =(49/10)*1/7*8*9 =7/8*9*10

1x2x3x4x5x6x7x8x9x10中2x5=10与10共2个0, 11x12x13x14x15x16x17x18x19x20中也有2个0, 1乘2乘3乘4乘5乘6乘7乘8乘9乘到20 共有2+2=4个0。

1/(5×6) + 1/(6×7) + 1/(7×8) = (1/5 - 1/6) + (1/6 - 1/7) + (1/7 - 1/8) = 1/5 - 1/8 = (8 - 5) / (5×8) = 3/40

提供个C的参考。 #include "stdio.h"int main(void){ int product,i; for(product=1,i=2;i

1×2×3×4×5×6×7×8×9×10 =1×2×4×8×3×6×9×7×5×10 =1×(2×2×2×2×2×2)×(3×3×3×3)×2×5×7×10 =3628800

1×2×3×4×5×6×7×8×9×10 =2×3×4×5×6×7×8×9×10 =6×4×5×6×7×8×9×10 =24×5×6×7×8×9×10 =120×6×7×8×9×10 =720×7×8×9×10 =5040×8×9×10 =40320×9×10 =362880×10 =3628800

2

把一加六分之一化成六分之七,以此类推,答案应该是20

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