Respostas

2014-05-03T09:30:13-03:00
F(t)= t²-7t
t² - 7t = 18
t² - 7t - 18 = 0 delta = 7² + 4.18 = 121
t = (-b + √delta)/2a
√121 = 11
t = (7 + 11)/2 = 9 horas (resp)