Question

The function h(t) = -4t^2 + 20t represents the height (in feet) of an athlete t seconds after pole vaulting. after how many seconds does the athlete reach his or her maximum height?

Answer 1

Answer:

2.5 seconds.

Step-by-step explanation:

h(t) = -4t^2 + 20t

= -4(t^2 - 5t)

Convert to vertex form by completing the square:

h(t) = -4[(t - 2.5t)^2 - 6.25]

     = -4(t - 2.5)^2 + 25    <--------- vertex form

So the vertex is at the point (2.5, 25).

So the athlete reaches the maximum height ( of 25 feet), after 2.5 seconds.