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5.11 Solving Optimization Problems

2 min readโ€ขjune 8, 2020

Sumi Vora

Sumi Vora


AP Calculus AB/BCย โ™พ๏ธ

279ย resources
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๐ŸŽฅWatch: AP Calculus AB/BC - Optimization Problems

Example Problem

A cylindrical soda can has the volume V = 32ฯ€ in^3. What is the minimum surface area of the can?ย ๐Ÿฅ›
First, letโ€™s list all of the variables that we have: volume (V), surface area (S), height (h), and radius (r)
Weโ€™ll need to know the volume formula for this problem. Usually, the exam will provide most of these types of formulas (volume of a cylinder, the surface area of a sphere, etc.), so you donโ€™t have to worry about memorizing them.ย 
First, letโ€™s try to find the relationships between all of the variables, and plugin what we know.ย 
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The question is asking us to minimize the surface area, so we have to take the derivative of S
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreenshot%20(523).png?alt=media&token=5992cfb9-939e-4e95-90ca-9688b8c24e36
There is an implicit domain of r>0, because it would be impossible to have a legitimate cylinder with a radius of 0 or a negative number.
r
0
...
0
...
dS/dr
0
-
2.52
+
Based on the sign chart, we know that 2.52 is the absolute minimum on the implicit domain, so the surface area is minimized when r = 2.52
Since the question is asking what the minimum surface area would be, we simply plug r into the surface area equationย 
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreenshot%20(525).png?alt=media&token=076cdaac-6605-433d-9ab1-76e94e72c634

Practice FRQ

On the AP exam, the examples may seem much more complex, but they will follow the same steps.ย 
You operate a tour service that offers the following rates for tours: $200 per person if the minimum number of people book the tour (50 people is the minimum), and for each person past 50 people up to a maximum of 80 people, the cost per person is decreased by $2. It costs you $6000 to operate the tour plus $32 per person.๐Ÿ’ตย 
  1. Write a function C(x) that represents the costย 
  2. Write a function R(x) that represents revenueย 
  3. Given that profit can be represented by P(x)=R(x)-C(x), write a function that represents profit and state the domain of the functionย 
  4. Find the number of people that maximizes the profit. What is the maximum profit?ย 
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreen%20Shot%202020-05-27%20at%207.22-aNI6PmjEpFJM.png?alt=media&token=f60c8aa5-7543-4470-8a71-ff44854745d9
Browse Study Guides By Unit
๐Ÿ‘‘Unit 1 โ€“ Limits & Continuity
๐Ÿค“Unit 2 โ€“ Fundamentals of Differentiation
๐Ÿค™๐ŸฝUnit 3 โ€“ Composite, Implicit, & Inverse Functions
๐Ÿ‘€Unit 4 โ€“ Contextual Applications of Differentiation
โœจUnit 5 โ€“ Analytical Applications of Differentiation
๐Ÿ”ฅUnit 6 โ€“ Integration & Accumulation of Change
๐Ÿ’ŽUnit 7 โ€“ Differential Equations
๐ŸถUnit 8 โ€“ Applications of Integration
๐Ÿฆ–Unit 9 โ€“ Parametric Equations, Polar Coordinates, & Vector-Valued Functions (BC Only)
โ™พUnit 10 โ€“ Infinite Sequences & Series (BC Only)
๐ŸงMultiple Choice Questions (MCQ)
โœ๏ธFree Response Questions (FRQ)
๐Ÿ“†Big Reviews: Finals & Exam Prep

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