даю 30 балов пж

Question

 даю 30 балов пж

Answer 1

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