初一数学 求学霸解答。

Question

如题所述

Answer 1

解答：
1/（X+4）+1/(X+7）=1/(X+5)+1/(X+6)
1/（X+4）-1/(X+5)=1/(X+6)-1/(X+7）
(x+5-x-4)/(x+4)(x+5)=(x+7-x-6)/(x+6)(x+7)
1/(x²+9x+20)=1/(x²+13x+42)
x²+9x+20=x²+13x+42
9x-13x=42-20
-4x=22
x=-11/2.追问

还有一题🙏

追答

(2x+3xy-4y)/(x-3xy-2y)
=(2/y+3-4/x)/(1/y-3-2/x)
=[3-4(1/x-1/2y)]/[-3-2(1/x-1/2y)]
=(3-4/3)/(-3-2/3)
=(9-4)/(-9-2)
=5/11

采纳

追问

我的天那 这什么啊😱

为何这么乱

抄否抄不了

Answer 2

1/(x+4)-1/(x+5)=1/(x+6)-1/(x+7)
[(x+5)-(x+4)/[(x+4)(x+5)]=[(x+7)-(x+6)]/[(x+6)(x+7)]
1/[(x+4)(x+5)]=1/[(x+6)(x+7)]
(x+6)(x+7)=(x+4)(x+5)
x^2+13x+42=x^2+9x+20
13x-9x=20-42
4x=-22
x=-5.5追问

还有一题🙏