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91Ó°ÊÓ

Use a double integral to prove that the area of the circle with radius R and equationr=2RcosθisπR2.

Short Answer

Expert verified

The area of the circle is

A=Ï€R2P

Step by step solution

01

Given information

The objective of this problem is to use double integral to prove that the area of the circle with radius R and equation r=2RcosθisπR2.

02

calculation

Draw the circle

Plot of r=2Rcosθ

Given circle is symmetrical about the horizontal axis. Therefore area of circle in polar form can be expressed as the twice of area of upper half circle.

A=2∫6a1∫5xrdrdθ

Here, θ1=0,θ2=π2andr1=0,r2=r

A=2∫0π/2∫0r-2πcosθrdrdθ

Integrate with respect to r first

A=2∫0*/2r2202πenedθ∫xndx=xn+1n+1+C

A=2∫0π/2(2Rcosθ)2-02

A=2R2∫0π/22cos2θdθA=2R2∫0π/2[1+cos2θ]dθ

Integrate with respect toθ

A=2R2θ+12sin2θ0x/2∫cosxdx=sinx+CA=2R2π2+12sinπ-0

localid="1650471847418" A=Ï€R2

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