Question

已知x的平方+xy=7,y的平方+xy=2,求x-y的值

Answer 1

x²+xy=7

y²+xy=2

x²+y²+2xy=9------(x+y)(x+y)=9

x²-y²=5-------------(x+y)(x-y)=5

(x-y)²=25/9

x-y=± 5/3