His average speed is 634/13 = 48,77 miles/hour. Well, he's fast :D
N³ - 2n² - 15n = 0
"n"
n (n² + 2n - 15) = 0
n = 0
n² + 2n - 15 = 0
Δ = (2)² - 4(1)(-15)
Δ = 4 + 60 = 64
n' = (-2+8) / 2 = 6/2 =3
n'' = (-2-8) / 2 = -10/2 = -5
Solution:
S {-5 , 0 , 3 }
