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9.9 Finding the Area of the Region Bounded by Two Polar Curves

1 min readโ€ขjune 8, 2020

Sumi Vora

Sumi Vora


AP Calculus AB/BCย โ™พ๏ธ

279ย resources
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Once you get the hang of finding the area under one curve, finding the area between two curves is pretty simple. Remember from previous units that when you find the area between two curves, you subtract the bottom curve from the top curve. This is the same in polar functions, but instead of subtracting โ€œtop minus bottom,โ€ youโ€™ll subtract โ€œouter minus inner.โ€ย 
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If the curves intersect, then you may have to find the area inside the curves by splitting the region.ย 
Example: Let R be the region inside the graph of the polar curve r = 4 and r = 4 + 2sin(2ฮธ) on [0, ฯ€]. Find the area of R.
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreenshot%20(1223).png?alt=media&token=3cbb074f-6dd1-4637-8b47-703d20fce87e
https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2FScreenshot%20(1225).png?alt=media&token=5b704619-dbe8-428c-ba50-144e5393f787
Since the graphs intersect at ฮธ = 2 we can see that when ฮธ < ฯ€/2, r = 4 is on top, and when ฮธ > ฯ€/2, r = 4+2sin(2ฮธ) is on top. Based on this information, we can construct two integrals:
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Polar Arc Lengthย 

There is one last thing you need to know about polar functions: arc length. Finding arc length is pretty straightforward, but you do need to have the formula memorized for the exam.ย 
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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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