www.5129.net > 1x2+2x3+3x4+4x5+5x6+6x7+7x8+8x9=

1x2+2x3+3x4+4x5+5x6+6x7+7x8+8x9=

3÷(3x4)x(4x5)÷(5x6)x(6x7)÷(7x8)x(8x9)=(3÷3)÷4×4×5÷5÷6×6×7÷7÷8×8×9=1×9=9

y=5x6+6x7+7x8+8x9+9x10+10x11+11x12 y=5*6+6*7+7*8+8*9+9*10+10*11+11*12 = 532

1/1x2+1/2x3+1/3x4+1/4x5+1/5x6+1/6x7+1/7x8+1/8x9+1/9x10 =1-1/2+1/2-1/3+1/3-....-1/9+1/9-1/10 =1-1/10 =9/10

1/4X5 + 1/5X6 + 1/6X7 + 1/7X8 + 1/8X9 + 1/9X10 = (1/4 - 1/5) + (1/5 - 1/6) + (1/6 - 1/7) + (1/7 - 1/8) + (1/8 -1/9) + (1/9 - 1/10) = 1/4 - 1/10 = 3/20

原式=1-1/2+1/2-1/3+1/4-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8+1/8-1/9 =1-1/9 =8/9

因为an=n*(n-1)/n+1 所以每个数可以看成2/3+(1+2/4)+(2+2/5)+(3+2/6)...+(8+2/11)= 1+2+3...+8+2/3+2/4+2/5...+2/11=36+2*(1/3+1/4+1/5+...1/11) 因为后面的那个是一个发散数列,好像没有求和公式,所以只能同分计算,当然可以把简单...

7/18

2/3x4x5+2/4x5x6+2/5x6x7+2/6x7x8+2/7x8x9+2/8x9x10=( ) =1/3*4-1/4*5+1/4*5-1/5*6+...+1/8*9-1/9*10 =1/3*4-1/9*10 =1/12-1/90 =13/180

1+2x3+4x5+6x7+8x9=4455 说明:在上面等号前加2个括号,使之等于4455 (1+2×3+4×5+6)×(7+8)×9==4455 7 7 7 7=10 在3个空处使用加减乘除 三个空处都要使用符号吗?如果都用,那应该没有答案.

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