(1/x-7)+(1/x-1)=(1/x-6)+(1/x-2)
1/(X-7)-1/(X-6)=1/(X-2)-1/(X-1)
(X-6-X+7)/[(X-7)(X-6)]=(X-1-X+2)/[(X-1)(X-2)]
X方-3X+2=X方-13X+42
10X=40
X=4
(1/x+a)-(1/x+b)=(1/x+c)-(1/x+d)
(X+B-X-A)/[(X+A)(X+B)]=(X+D-X-C)/[(X+C)(X+D)]
B-A=D-C
X方+(A+B)X+AB=X方+(C+D)X+CD
X=(CD-AB)/(A+B-C-D)