bjr
h(t) = -5t² + 100t
h(t) - 320 = -5t² + 100t - 320 = -5 (t² - 20t + 64)
racines de t² - 20t + 64 :
Δ = (-20)² - 4*1*64 = 400 - 256 = 144 = 12²
donc t1 = (20 + 12)/2 = 16
et t2 = (20-12)/2 = 4
=> -5 (t² - 20t + 64) = -5 (t-4) (t-16) = (-5t+80) (t-4)