Question

已知，x-3y=0,求x2次方-2xy+y的2次方分之2x+y乘（x-y)的值

Answer 1

带入x=3y,分母为9y^2-6y^2+y^2=4y^2.分子为7y*2y=14y^2.所以原式=7/2.

Answer 2

由题设得 x=3y
∴原式=[(2x+y)(x-y)]/(x-y)²=(2x+y)/(x-y)=(7y)/(2y)=7/2