急求高人解答 数学题!（1+1/11+1/13+1/17）x(1/11+1/13+1/17+1/19)-(1+1/11+1/13+1/17+1/19)x(1/11+1/13+1/17)=?
问题描述：
急求高人解答 数学题!
（1+1/11+1/13+1/17）x(1/11+1/13+1/17+1/19)-(1+1/11+1/13+1/17+1/19)x(1/11+1/13+1/17)=?
答
换元法吧，换元方式也很多，这里就设a=1+1/11+1/13+1/17
那么原式=a(a+1/19-1)-(a+1/19)(a-1)
=a²+a/19-a-(a²-a+a/19-1/19)
=1/19
答
[1+(1/11+1/13+1/17）]x[(1/11+1/13+1/17)+1/19]=(1/11+1/13+1/17)+(1/11+1/13+1/17)^2+1/19+(1/11+1/13+1/17)/19[1+(1/11+1/13+1/17)+1/19]x(1/11+1/13+1/17)= (1/11+1/13+1/17)+(1/11+1/13+1/17)^2+(1/11+1/13+1/1...