1/(x-10)+1/(x-6)=1/(x-7)+1/(x-9)
1/(x-10)-1/(x-9)=1/(x-7)-1/(x-6)
[(x-9)-(x-10)]/(x-10)(x-9)=[(x-6)-(x-7)]/(x-7)(x-6)
即是
1/（x-9)(x-10)=1/(x-6)(x-7)
x^2-13x+42=x^2-19x+90
6x=68
得出：x=8