✔ 最佳答案
9 = -16t^2 + 24t + 4
16t^2 - 24t - 4 + 9 = 0
16t^2 - 24t + 5 = 0
16t^2 - 4t - 20t + 5 = 0
(16t^2 - 4t) - (20t - 5) = 0
4t(4t - 1) - 5(4t - 1) = 0
(4t - 1)(4t - 5) = 0
4t - 1 = 0
4t = 1
t = 1/4 (0.25)
4t - 5 = 0
4t = 5
t = 5/4 (1.25)
∴ t = 1/4 (0.25), 5/4 (1.25)