find the least value of m?

二次不等式解法：
(x - 大)(x - 小) < 0 ⇔ 小 < x < 大
(x - 大)(x - 小) > 0 ⇔ x > 大 or x < 小

T(1) = a = 3 and d = 2
T(n) = a + (n - 1)d = 3 + (n - 1)(2) = 2n + 1
S(n) = n/2[2a + (n - 1)d] = n/2[2(3) + (n - 1)(2)] = n(3 + n - 1) = n(n + 2)

Therefore,
S(m) > 6888
m(m + 2) > 6888
m² + 2m - 6888 > 0
(m - 82)(m + 84) > 0
m > 82 or m < -84