Question

已知X,Y满足x+y=4,x^2-y^2=20,求x,y的值

Answer 1

x^2-y^2=20

(x+y)(x-y)=20

x+y=4

4(x-y)=20

所以 x-y=5

所以2x=9

2y=-1

所以

x=9/2,y=-1/2

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