(1×1+2×2)⼀1×2+(2×2+3×3)⼀2×3+(3×3+4×4)⼀3×4+···+(20

2024-12-13 04:35:13
推荐回答(1个)
回答1:

上式=(1+2)的平方 /1*2 再减去2
每个式子都这样换
得=9/(1*2)+25/(2*3)+49/(3*4)+......4007*4007/(2011*2012) -2*2012 =(4+1/2)+(4+1/6)+(4+1/12)+......+(4+1/2011*2012) -2*2011 =4*2011+(1/2+1/6+1/12+......+1/2011*2012)-2*2011
=2*2011 +(1-1/2+ 1/2-1/3 +1/3-1/4 +1/2011-1/2012)
=4022+(1-1/2012)
=4022+2011/2012
呵呵个点加分舍
亲,给个好评吧