Persamaan kuadrat x2 + (m – 10)x + 64 = 0 mempunyai akar kembar. Jika m < 0, maka nilai 3m – 1 = ... .

Akar kembar >> b² - 4ac = 0
(m-10)² - 4.1.64 = 0
m² - 20m + 100 - 256 = 0
m² - 20m - 156 = 0
(m-26)(m+6) = 0
m1 = 26
m2 = -6

karena m < 0 maka nilai m = -6
3m - 1 = 3(-6) - 1 = -19