求和[x+(1/y)]+[x^2+(1/y^2)]+...+[x^n+(1/y^n)] (其中x≠0,x≠0,y≠1)
问题描述：
求和[x+(1/y)]+[x^2+(1/y^2)]+...+[x^n+(1/y^n)] (其中x≠0,x≠0,y≠1)
答
[x+(1/y)]+[x^2+(1/y^2)]+...+[x^n+(1/y^n)]=(x+x^2+……+x^n)+(1/y+1/y^2+……+1/y^n)x+x^2+……+x^n是以x为首项,x为公比的等比数列,有x项所以和=x(x^n-1)/(x-1)1/y+1/y^2+……+1/y^n是以1/y为首项,1/y为公比的等比...