巧算:(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4+1/5+1/6)-(1+1/2+1/3+1/4+1/5+1/6)*(1/2+1/3+1/4+1/5)(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4+1/5+1/6)-(1+1/2+1/3+1/4+1/5+1/6)*(1/2+1/3+1/4+1/5)=====
来源:学生作业学帮网 编辑:学帮网 时间:2024/05/13 08:08:54
巧算:(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4+1/5+1/6)-(1+1/2+1/3+1/4+1/5+1/6)*(1/2+1/3+1/4+1/5)
(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4+1/5+1/6)-(1+1/2+1/3+1/4+1/5+1/6)*(1/2+1/3+1/4+1/5)
=
=
=
=
=
为方便书写,设1/2+1/3+1/4+1/5=t,则
(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4+1/5+1/6)-(1+1/2+1/3+1/4+1/5+1/6)*(1/2+1/3+1/4+1/5)
=(t+1)*(t+1/6)-(1+t+1/6)*t
=(t²+1/6t+t+1/6)-(t+7/6)*t
=(t²+7/6t+1/6)-(t²+7/6t)
=t²+7/6t+1/6-t²-7/6t
=1/6
设(1+1/2+1/3+1/4+1/5)=A
(1/2+1/3+1/4+1/5)=B
就是把这两个式子当成一个整体来看
令:(1+1/2+1/3+1/4+1/5)=a;
(1+1/2+1/3+1/4+1/5)*(1/2+1/3+1/4+1/5+1/6)-(1+1/2+1/3+1/4+1/5+1/6)*(1/2+1/3+1/4+1/5)
=a(a-1+1/6)-(a+1/6)(a-1)
=a²-a+a/6-a²+a-a/6+1/6
=1/6
巧算(1- 1/2 )( 1/3 -1)(1- 1/4 )( 1/5 -1)…( 1/2003 -1)(1- 1/2004 )
巧算:1/1*2+1/2*3+1/3*4+.+1/99*100等于多少?
巧算;1/2*1+1/2*3+1/3*4+.1/56*57
巧算1/1×2+1/2×3+1/3×4+…1/49×50
1×2/1+2×3/1+3×4/1+4×5/1+5×6/1巧算
巧算 1/1×2+1/2×3 +1/3×4 +1/4×5 +…+ 1/19×20
巧算24点1:3:4:6
巧算:1/1*2+1/2*3+1/3*4+……1/19*20+1/20*21=
巧算24点1,2,4,7
巧算24点1,2,4,7
巧算 (3+1)(3^2+1)(3^4+1)(3^5+1)……(3^2n+1)快
巧算:【1+2分之1】*【1+3分之1】*【1+4分之1】*.*【1+8分之1】*【1+9分之1】*【1+10分之1】
巧算((2^1+1)(2^2+1)(2^4+1)(2^8+1)+1)/2^15
20-19+18-17+.+4-3+2-1巧算
巧算 50-49+48-47+.+4-3+2-1=
巧算1+2+3+4+5.+50等于多少
巧算:50-49+48-47+…+4-3+2-1
巧算; 1+6+8+4+2+7+3+9=