已知x/y=3那么(x²+2xy-3y²)/(x²-xy+y²)
=[(x/y)²+2x/y-3]/[(x/y)²-x/y+1]
=(3²+2*3-3)/(3²-3+1)
=12/7
如果不懂,请Hi我,祝学习愉快!