Question

若xy=1/2,求代数式3(x+y)^2/3(x-y)^2的值

Answer 1

3(x+y)^2/3(x-y)^2

3(x+y)²/3(x-y)²=(x²+2xy+y²)/(x²-2xy+y²)

把xy=1/2代入上式：原式=[x²+2×（1/2）+y²]/[x²-2×（1/2）+y²]

=-1