This is quite old thread!
I was going to quote the posters to see if my answer is correct, but I doubt they'd come on anymore!
I think this is what you do:
16−(x−4)2The maximum value of
8x−x2 is -16.
The maximum value of
x is 4.
The general formula for completing squares is:
a(x+h)2+ka is the maximum, but this needs to be a negative number. If the
a value in the equation if negative, leave it as it is, if it is positive, change it to negative.
h is your maximum value for
x.
k is the maximum value for
y.
So in this equation, the maximum coordinates are
(4,0) because there is no
k value therefore it must be 0. It is 4 not -4 because you're meant to do the opposite of what is in the brackets, like how
y=f(x+2) you move to the left rather than to the right and how
y=f(2x) is actually a stretch by scale factor
21.
So the answers are 16 and 4.
I'm not 100% sure on this though...
(This is based upon
this post on yahoo answers.)
Other links:
WikipediaYoutubeEdit: Now I've just confused myself about maximum and minimum - although I've found the answers and this is correct, however it seems that many sources online say this is how you work out a minimum? :/