Algebra
posted by Laura on .
I am supposed to find the ticket sales of a concert using this formula:
N(x)= 0.3x^2 + 6x + 15
X represtents the number of days since the concert was first announced. I need to find out when daily ticket sales will peak and how many tickets will be sold on that day. How do i work out this problem I don't know the first place to start! please help.

If you are not in Calculus, then I would graph the equation to find x for the maximum sales.

So I should find the vertex?

I assume no calculus, therefore we must look at the shape of this curve.
it is of form ax^2 + bx + c, a parabola
y = .3 x^2 + 6 x + 15
we need to find the vertex
complete the square
y/.3 = x^2 +6/.3 x +15/.3
x^2  20x 50 = 3.33 y
x^2 20 x = 3.33 y +50
x^2 20 x +100 = 3.33y +150
(x10)^2) = 3.33 ( y  45)
vertex at (10,45)
10 days, 45 tickets