# Finding a maximum height. (Polynomial function)

• Mar 7th 2011, 01:21 PM
msinger23
Finding a maximum height. (Polynomial function)
Hi, I have the correct answer but I am not sure how I got it:

The path of a diver is given by

y= -4/9x^2 + 24/9x + 12 where y is the height (in feet) and x is the horizontal distance from the end of the diving board (in feet). What is the maximum height of the diver?

Ok, so I used this formula : -b/2a (the vertex) to get x = 3. Apparently that is the answer, but I'm curious as to why they wouldn't plug 3 as the x value to get the height. Any help is appreciated. Thanks.
• Mar 7th 2011, 02:39 PM
topsquark
Quote:

Originally Posted by msinger23
Hi, I have the correct answer but I am not sure how I got it:

The path of a diver is given by

y= -4/9x^2 + 24/9x + 12 where y is the height (in feet) and x is the horizontal distance from the end of the diving board (in feet). What is the maximum height of the diver?

Ok, so I used this formula : -b/2a (the vertex) to get x = 3. Apparently that is the answer, but I'm curious as to why they wouldn't plug 3 as the x value to get the height. Any help is appreciated. Thanks.

The problem statement is asking for the maximum height, so you are correct in saying we need to find y(3). Beware though that many problems like this only ask for where the max height is. In this case it looks like a typo on the book's part as it seems they only want the location (x = 3) and not the actual height y(3) that they are actually asking for.

-Dan