Question

(3x-4y)^2-(3x+y)^2

(3x-4y)^2-(3x+y)^2
(x+1/2y-3)(x-1/2y+3)
已知x+y=5,X^2-Y^2=15,求x-y的值

是 x加二分之一y减去3
你们的答案我看不懂~
好多不一样的%……

Answer 1

求什么？
(3x-4y)^2-(3x+y)^2
=[(3x-4y)+(3x+y)][(3x-4y)-(3x+y)]
=(6x-3y)(-5y)
=-15y(2x-y)

(x+1/2y-3)(x-1/2y+3)
=[x+(1/2y-3)][x-(1/2y-3)]
=x^2 - (1/2y-3)^2
=x^2 - 1/4y^2 + 3y - 9

x^2 - y^2 = (x+y)(x-y)=5(x-y)=15
x-y=3

Answer 2

1、（3x-4y)^2-(3x+y)^2=(3x-4y-3x-y)(3x-4y+3x+y)=5y(6x-3y)...刚算错了

2、1/2y是个整体表示（y/2）吧？把(y/2)-3看成一个整体
x^2-[(y/2)-3]^2=x^2-(y^2)/4+3y-9

已知x+y=5,X^2-Y^2=15,求x-y的值
x^2-y^2=(x-y)(x+y)=5(x-y)=15
x-y=3

Answer 3

(3x-4y)^2-(3x+y)^2
=(3x-4y+3x+y)*(3x-4y-3x-y)
=(6x-3y)*(-5y)
=-15*(2x-y)*y
=-30xy+15y^2

(x+1/2y-3)(x-1/2y+3)
=(x+(1/2y-3))*(x-(1/2y-3))
=x^2-(1/2y-3)^2
还短一步自己做吧，不确定你是1/（2y）还是y/2