1.已知1/x+1/y=5,则分式/的值为:

1/x+1/y=5[x+y]/xy=5x+y=5xy/=[2(x+y)-3xy]/[5xy+2xy]=[2*5xy-3xy]/[7xy]=7xy/7xy=1x/[x^2+x+1]=1/3[x^2+x+1]/x=3x+1/x+1=3x+1/x=2[x^4+x^2+1]/x^2=x^2+1/x^2+1=[x+1/x]^2-2+1=2*2-1=3所以：x^2/[x^4+x^2+1]=1/3