Question

已知y分之x=2,求x^2+2xy-3y^2分之x^2-9y^2的值

Answer 1

x/y=2

x=2y

原式=(x+3y)(x-3y)/(x+3y)(x-y)

=(x-3y)/(x-y)

=(2y-3y)/(2y-y)

=-y/y

=-1