Difference between revisions of "009B Sample Final 1, Problem 1"

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|We need to set these two equations equal in order to find the intersection points of these functions.
 
|We need to set these two equations equal in order to find the intersection points of these functions.
 
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|So, we let <math style="vertical-align: -6px">2(-x^2+9)=0</math>. Solving for <math>x</math>, we get <math>x=-3,3</math>.
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|So, we let <math style="vertical-align: -5px">2(-x^2+9)=0</math>. Solving for <math style="vertical-align: 0px">x</math>, we get <math style="vertical-align: 0px">x=\pm 3</math>.
 
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|This means that we need to calculate the Riemann sums over the interval <math>[-3,3]</math>.
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|This means that we need to calculate the Riemann sums over the interval <math style="vertical-align: -5px">[-3,3]</math>.
 
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!Step 2: &nbsp;
 
!Step 2: &nbsp;
 
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|Since the length of our interval is <math style="vertical-align: 0px">6</math> and we are using <math style="vertical-align: 0px">3</math> rectangles,
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|Since the length of our interval is <math style="vertical-align: 0px">6</math> and we are using <math style="vertical-align: -1px">3</math> rectangles,
 
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|each rectangle will have width <math style="vertical-align: 0px">2</math>.  
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|each rectangle will have width <math style="vertical-align: 0px">2</math>&thinsp;.  
 
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|Thus, the lower Riemann sum is
 
|Thus, the lower Riemann sum is
 
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::<math>2(f(-3)+f(-1)+f(3))=2(0+16+0)=32</math>.
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::<math>2(f(-3)+f(-1)+f(3))\,=\,2(0+16+0)\,=\,32.</math>
 
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Revision as of 12:26, 25 February 2016

Consider the region bounded by the following two functions:

and .

a) Using the lower sum with three rectangles having equal width, approximate the area.

b) Using the upper sum with three rectangles having equal width, approximate the area.

c) Find the actual area of the region.

Foundations:  
Recall:
1. The height of each rectangle in the lower Riemann sum is given by choosing the minimum Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle y} value of the left and right endpoints of the rectangle.
2. The height of each rectangle in the upper Riemann sum is given by choosing the maximum Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle y} value of the left and right endpoints of the rectangle.
3. The area of the region is given by Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \int_a^b y~dx} for appropriate values Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle a,b} .

Solution:

(a)

Temp1

Step 1:  
We need to set these two equations equal in order to find the intersection points of these functions.
So, we let Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 2(-x^2+9)=0} . Solving for Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle x} , we get Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle x=\pm 3} .
This means that we need to calculate the Riemann sums over the interval Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle [-3,3]} .
Step 2:  
Since the length of our interval is Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 6} and we are using Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 3} rectangles,
each rectangle will have width Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 2}  .
Thus, the lower Riemann sum is
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 2(f(-3)+f(-1)+f(3))\,=\,2(0+16+0)\,=\,32.}

(b)

Temp2

Step 1:  
As in Part (a), the length of our inteval is Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 6} and
each rectangle will have width Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 2} . (See Step 1 and 2 for (a))
Step 2:  
Thus, the upper Riemann sum is
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 2(f(-1)+f(-1)+f(1))=2(16+16+16)=96}

(c)

Temp3

Step 1:  
To find the actual area of the region, we need to calculate
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \int_{-3}^3 2(-x^2+9)~dx}
Step 2:  
We integrate to get
Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \begin{array}{rcl} \displaystyle{\int_{-3}^3 2(-x^2+9)~dx} & = & \displaystyle{2\bigg(\frac{-x^3}{3}+9x\bigg)\bigg|_{-3}^3}\\ &&\\ & = & \displaystyle{2\bigg(\frac{-3^3}{3}+9\times 3\bigg)-2\bigg(\frac{-(-3)^3}{3}+9(-3)\bigg)}\\ &&\\ & = & \displaystyle{2(-9+27)-2(9-27)}\\ &&\\ & = & \displaystyle{2(18)-2(-18)}\\ &&\\ & = & \displaystyle{72}\\ \end{array}}

Temp4

Final Answer:  
(a) Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 32}
(b) Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 96}
(c) Failed to parse (MathML with SVG or PNG fallback (recommended for modern browsers and accessibility tools): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 72}

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