[tex] \frac{1}{х+1} - \frac{1}{х-6} = \frac{7}{12} [/tex] даю 30 балов пж 

1/(n+1) - 1/(n-6) =7/12      /.12(n+1)(n-6), n≠-1, n≠612(n-6)-12(n+1)=7(n+1)(n-6)12n-72-12n-12=7(n²-6n+n-6)-84=7n²-35n-427n²-35n-42+84=07n²-35n+42=0    /:7n²-5n+6=0(n-2)(n-3)=0a)n-2=0, n=2b)n-3=0,n=3