40^x=2000,x=log40(2000),所以1/x=log2000(40)
50^y=2000,y=log50(2000),所以1/y=log2000(50)
所以(1/x)+(1/y)=log2000(40)+log2000(50)=log2000(40*50)=log2000(2000)=1