Question

solve for n 2 + 5 + 8 + 11 + n is equal to 345

Answer 1

Sn=$(n \div 2) \times (2.a1 + (n - 1).d = 345$
$(n \div 2).(2.2 + 3n - 3) = 345$
$(n \div 2).(3n + 1) = 345$
$3n ^{2} + n = 690$
$3n^{2} + n - 690 = 0$