1. ## Quadratic Formula Question #3

http://i.imgur.com/kPBi5Ueh.jpg

#15

I am not good at creating equations off of word problems... I try but I always get it wrong, I'm not sure how to do any word problems like these.

275x^2 - 15x - 19600 = 0

That equation was my attempt at it, not sure if it is correct...

Any help would be great, thanks!

2. ## Re: Quadratic Formula Question #3

if R is the revenue, S is the number of sales and P is the price. R=SP
When the price is decreased by \$15 x times the price is 275-15x and the sales is 90+5x.
You want to find x when R>19600

3. ## Re: Quadratic Formula Question #3

Shakarri has given the correct direction. Form the equation for R
you will get R = x^2+104x-206
Now proceed to differentiate to get min value of x.

4. ## Re: Quadratic Formula Question #3

Since this question is posted in the Pre-Calculus forum, you may not know how to use differential calculus to optimize a function. In this case, since you have a quadratic, look for the axis of symmetry.