1/2×3×4+1/3×4×5……1/19×20×21
来源:学生作业帮 编辑:大师作文网作业帮 分类:数学作业 时间:2024/10/06 06:46:34
1/2×3×4+1/3×4×5……1/19×20×21
1/2×3×4+1/3×4×5……1/19×20×21
=[1/(2×3)-1/(3×4)]×1/2+[1/(3×4)-1/(4×5)]×1/2+[1/(4×5)-1/(5×6)]×1/2+.+[1/(19×20)-1/(20×21)]×1/2
=1/2×[1/(2×3)-1/(3×4)+1/(3×4)-1/(4×5)+1/(4×5)-1/(5×6)+.+1/(19×20)-1/(20×21)]
=1/2×[1/(2×3)-1/(20×21)]
=1/2×(70/420-1/420)
=1/2×69/420
=69/840
=23/280
=[1/(2×3)-1/(3×4)]×1/2+[1/(3×4)-1/(4×5)]×1/2+[1/(4×5)-1/(5×6)]×1/2+.+[1/(19×20)-1/(20×21)]×1/2
=1/2×[1/(2×3)-1/(3×4)+1/(3×4)-1/(4×5)+1/(4×5)-1/(5×6)+.+1/(19×20)-1/(20×21)]
=1/2×[1/(2×3)-1/(20×21)]
=1/2×(70/420-1/420)
=1/2×69/420
=69/840
=23/280
1-2+3-4+5-6+……+19-20+21=?
巧算:1/1*2 + 1/2*3 + 1/3*4 +1/4*5 ……+ 1/19*20 +1/20*21 .
巧算:1/1*2+1/2*3+1/3*4+……1/19*20+1/20*21=
23+22+21+20……+1+1+2+3+4+5……+55
1-2+3-4+5-6+7-…+19-20+21小学题
1+2+3+4+5+…+18+19+20=
1×2+2×3+3×4+4×5+5×6+……+19×20
计算:[1/4(1^4+3^4+5^4+……+19^4)]/[1/4(2^4+4^4+6^4+……+20^4)]
1*2/5+2*3/5+3*4/5+……+19*20/5(简便计算,
1/2*3*4+1/2*3*4+3*4*5+……1/18*19*20=
算式(3/1-4/1)+(4/1-5/1)……+(20/1-19/1)求解
1/1*2*3+1/2*3*4+1/3*4*5+……+20*21*22=?