✔ 最佳答案
The big question is if this is a calculus class or not. Depending on that answer, I'd solve it differently. Presuming it's not, I'll solve this by putting it into vertex form:
h(t) = a(t - h) + k
When in this form, "k" is your answer as the maximum height:
h(t) = -16t² + 68t
I need t²'s coefficient to be 1, so divide both sides by -16:
-h(t)/16 = t² - (17/4)t
Now that we're in this format, we can complete the square on the right side by taking half of t's coefficient and squaring it. Then add that to both sides. So add 289/64 to both sides:
289/64 - h(t)/16 = t² - (17/4)t + 289/64
Now the right side can be factored as a perfect square trinomial:
289/64 - h(t)/16 = (t - 17/8)²
This tells us that the maximum height is reached at 17/8 seconds (2.125 seconds)
Now solve for h(t) again, keeping the binomial square in tact:
-h(t)/16 = (t - 17/8)² - 289/64
h(t) = -16(t - 17/8)² + 289/4
So 289/4 feet (72.25 ft) is the maximum height.