Posted by gabriel on Friday, January 18, 2013 at 6:29pm.
Sketch the problem
You need 5 lengths of fence of length w and 1 length e for end
area = A = w e
5 w + e = 90
5 w + A/w = 90
5 w^2 - 90 w + A = 0
where did you get 5?
Now if you do not know calculus, find the vertex of the parabola by completing the square
5 w^2 - 90 w = -A
w^2 - 18 w = -A/5
w^2 -18 w + 81 = -A/5 + 81
(w-9)^2 = -(1/5)(A - 405)
so max at w = 9 , A = 405
then
5 (9) + e = 90
45 + e = 90
e = 45
so 45 by 9
i know how to get the vertex and all the other stuff,
i just don't understand where did you get 5?
To get 5, DRAW A Picture
9 foot fence at 0, 11.25 , 22.5 , 33.75 , 45
and a 45 foot fence across the end
four fence sections requires five posts :)
because you need one at the start, zero.
(unless you close the figure topologically by joining the last section to the first.)
aah ok.. thanks a lot!!!;)
0, 11.25 , 22.5 , 33.75 , 45
notice four commas seperating five numbers
I am belaboring this because it is not the last time you will have to think about it.
ok,i will just try it myself so that i can understand it.. thanks..