15.3 Express an integral for finding the area of region bounded by:

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Discussion Overview

The discussion revolves around expressing an integral to find the area of a region bounded by three curves: \(y=2\sqrt{x}\), \(3y=x\), and \(y=x-2\). Participants explore different methods of integration, including single and double integrals, and the potential for using polar coordinates.

Discussion Character

  • Exploratory
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant expresses the area as a sum of two integrals: \(\int_0^3 2\sqrt{x} - \frac{x}{3} \, dx + \int_3^{4+2\sqrt{3}} 2\sqrt{x} - (x-2) \, dx\).
  • Another participant inquires about the possibility of iterating the problem into a double integral.
  • A response confirms that the area can be expressed as a double integral using vertical strips: \(A=\int_0^3\int_{x-2}^{2\sqrt{x}}\,dy\,dx+\int_3^{4+2\sqrt{3}}\int_{\frac{x}{3}}^{2\sqrt{x}}\,dy\,dx\).
  • There is a question about expressing the integrals using horizontal strips, with a participant noting that the current formulation consists of two integral sets added together.
  • A later reply suggests that expressing the area as a single integral may require a translation and conversion to polar coordinates.

Areas of Agreement / Disagreement

Participants express differing views on the best method to represent the area, with some favoring the use of double integrals and others questioning the necessity of multiple integrals. No consensus is reached on a single integral formulation.

Contextual Notes

Participants discuss the limitations of their current approaches, including the need for potential transformations to polar coordinates and the challenges of expressing the area with a single integral.

karush
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ok so there are 3 peices to this
Express and integral for finding the area of region bounded by:

\begin{align*}\displaystyle
y&=2\sqrt{x}\\
3y&=x\\
y&=x-2
\end{align*}

View attachment 7250
 

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Re: 15.3 Express and integral for finding the area of region bounded by:

karush said:
ok so there are 3 peices to this
Express and integral for finding the area of region bounded by:

\begin{align*}\displaystyle
y&=2\sqrt{x}\\
3y&=x\\
y&=x-2
\end{align*}

http://mathhelpboards.com/attachments/calculus-10/7250-15-3-express-integral-finding-area-region-bounded-15-3-png

$3y=x \implies y = \dfrac{x}{3}$

first intersection ...

$x-2 = \dfrac{x}{3} \implies x = 3$

second intersection ...

$x-2 = 2\sqrt{x} \implies x=4+2\sqrt{3}$
$\displaystyle A = \int_0^3 2\sqrt{x} - \dfrac{x}{3} \, dx + \int_3^{4+2\sqrt{3}} 2\sqrt{x} - (x-2) \, dx$
 
Re: 15.3 Express and integral for finding the area of region bounded by:

i was courious if this could be iterated into a double integral
 
Re: 15.3 Express and integral for finding the area of region bounded by:

karush said:
i was courious if this could be iterated into a double integral

Yes. First, since we are simply finding the area $A$ bounded by $R$, the integrand will be 1. Using vertical strips, and the work already provided by skeeter, we could write:

$$A=\int_0^3\int_{x-2}^{2\sqrt{x}}\,dy\,dx+\int_3^{4+2\sqrt{3}}\int_{\frac{x}{3}}^{2\sqrt{x}}\,dy\,dx$$

Can you write the intergrals using horizontal strips?
 
Re: 15.3 Express and integral for finding the area of region bounded by:

MarkFL said:
Yes. First, since we are simply finding the area $A$ bounded by $R$, the integrand will be 1. Using vertical strips, and the work already provided by skeeter, we could write:

$$A=\int_0^3\int_{x-2}^{2\sqrt{x}}\,dy\,dx+\int_3^{4+2\sqrt{3}}\int_{\frac{x}{3}}^{2\sqrt{x}}\,dy\,dx$$

Can you write the intergrals using horizontal strips?

but isn't this still 2 integral sets just added together ??
 
Re: 15.3 Express and integral for finding the area of region bounded by:

karush said:
but isn't this still 2 integral sets just added together ??

Yes, but given the nature of the bounded region, there is no way I know of to express it as a single integral without a translation and conversion to polar coordinates.

We could translate everything down 1 unit and 3 units to the left:

View attachment 7265

Can you determine the limits in polar coordinates?
 

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