若x-y=2(x+y),求代数式x-y/x+y+x+y/x-y

题目

若x-y=2(x+y),求代数式x-y/x+y+x+y/x-y
求代数式 x+y分之x-y+x-y分之x+y
已知:y=ax的3次方+bx+3,当x=-1/2时,y=-7,试求x=1/2时,y的值

答案

(x-y)/(x+y)+(x+y)/(x-y)
x-y=2(x+y),(x-y)/(x+y)=2,(x+y)/(x-y)=1/2
(x-y)/(x+y)+(x+y)/(x-y)=2+1/2=5/2