1/(x+5)(x+6) +1/(x+6)(x+7) +1/(x+7)(x+8) =3/70 ;
(1/(x+5) -1/(x+6)) +(1/(x+6) -1(x+7))+(1/(x+7) -1/(x+8)) = 3/70 ;
1/(x+5) -1/(x+8)) = 3/70 ;
3/(x+5)(x+8) =3/70 ;
(x+5)(x+8) =70 ; || (-10)*(-7) или 7*10 ||
x² +13x -30 =0 ;
D =13² -4(-30) =169+120 =289 =17².
x ₁= (-13 -17)/2 = -15 ;
x₂ =(-13+17)/2 =2.
ответ: {-15 ; 2}.