Question

（1）已知x^2+3xy-4y^2=0,求(x+2y)分之x-2y的值

Answer 1

1:x^2+3xy-4y^2=0

(x-y)(x+4y)=0

x=y,x=-4y

(x+2y)分之(x-2y)=-1/3 或-3

2:,（x^2+y^2)(x^2-1+y^2)=12

令x²+y²=a

a(a-1)=12

(a-4)(a+3)=0

a=4,a=-3(舍去)

x^2+y^2=4