快乐叮叮
幼苗
共回答了10个问题采纳率:90% 举报
1.1/x-1/y=3,得(y-x)/xy=3,则y-x=3xy
所以(2x-14xy-2y)/(x-2xy-y)= 2(x-y-7xy)/(x-y-2xy)=-20xy/(-5xy)=4
2.原式=2/(1-x^2)+2/(1+x^2)+4/(1+x^4)=4/(1-x^4)+4/(1+x^4)=8/(1-x^8)
3.x/3=y/1=z/2,所以x=3y,z=2y
所以2(x^2)+2(y^2)+5(z^2)/xy+yz+zx=40y^2/11y^2=40/11
1年前
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