.
The revenue will be maximized when the quadratic function
r(p) = =-2.5p^2 + 800p
will get the maximum.
It will happen when p = = = 160 dollars.
It is optimal price for dvd player.
And the maximum revenue then will be then -2.5*160^2 + 800*160 = 64000 dollars.
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On finding the maximum/minimum of a quadratic function see the lessons in this site
- HOW TO complete the square to find the minimum/maximum of a quadratic function
- Briefly on finding the minimum/maximum of a quadratic function
- HOW TO complete the square to find the vertex of a parabola
- Briefly on finding the vertex of a parabola
Also, you have this free of charge online textbook in ALGEBRA-I in this site
- ALGEBRA-I - YOUR ONLINE TEXTBOOK.
The referred lessons are the part of this textbook under the topic "Finding minimum/maximum of quadratic functions".
Save the link to this online textbook together with its description
Free of charge online textbook in ALGEBRA-I
https://www.algebra.com/algebra/homework/quadratic/lessons/ALGEBRA-I-YOUR-ONLINE-TEXTBOOK.lesson
to your archive and use it when it is needed.