Question

Solutions: m = −2, m = −8, m = −8

solve

Answer 1

If the solutions are m = −2, m = −8 (double), the cubic equation with those roots is
(m + 2)(m + 8)^2 = 0.

Expand:
(m + 8)^2 = m^2 + 16m + 64
(m + 2)(m^2 + 16m + 64) = m^3 + 18m^2 + 96m + 128 = 0.

Solve by factoring:
(m + 2)(m + 8)^2 = 0 ⇒ m = −2 or m = −8 (with multiplicity 2).