query 9 

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course mth 272

If your solution to a stated problem does not match the given solution, you should self-critique per instructions at

http://vhcc2.vhcc.edu/dsmith/geninfo/labrynth_created_fall_05/levl1_22/levl2_81/file3_259.htm.

Your solution, attempt at solution: If you are unable to attempt a solution, give a phrase-by-phrase interpretation of the problem along with a statement of what you do or do not understand about it. This response should be given, based on the work you did in completing the assignment, before you look at the given solution.

009. `query 9

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Question: `q 5.5.1 (previously 5.5.6 (was 5.5.6) ) area between (x-1)^3 and x-1 from 0 to 2

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Your solution:

x-1 = (x-1) - (x-1)^3

(x-1)^3 = (x-1)^3 - (x-1)

confidence rating #$&*:2

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Given Solution:

`a The graphs cross at (0, -1), (1,0), and (2, 1) as we easily find by solving the equation (x-1)^3 = (x - 1).

Since (1, 0) lies between the endpoints of our interval we have to be careful about which function lies above which, and we'll have to split the calculation into two separate intervals.

• The x-1 graph lies above the (x-1)^3 graph from 0 to 1, so the area on this interval will be the integral of (x-1) - (x-1)^3 between these limits.

• The (x-1)^3 graph lies above the (x-1) graph from 1 to 2, so the area on this interval will be the integral of (x-1)^3 - (x-1) between these limits.

Each integral is equal to .25, so the total area is the sum .25 + .25 = .5 of these areas. **

DER

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Self-critique (if necessary):

Didn’t know how you wanted me to write it down.

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Self-critique Rating:

@& A short paragraph explaining your thinking would be good.

It isn't clear what your equations

x-1 = (x-1) - (x-1)^3

(x-1)^3 = (x-1)^3 - (x-1)

mean or what you were thinking when you wrote them down.

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Question: `q 5.5.2 (previously 5.5.10 (was 5.5.10) ) describe the region for integral of (1-x^2) - (x^2-1) from -1 to 1

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Your solution:

It is not a perfect circle but it is very close.

confidence rating #$&*:3

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Given Solution:

`a*& The graph of 1 - x^2 is an upside down parabola with vertex at (0, 1), intercepting the x axis at x = -1 and x = 1.

The graph of x^2 - 1 is a rightside up parabols with vertex at (0, -1), intercepting the x axis at x = -1 and x = 1.

The region between the graphs is close to a circle passing thru (-1,0), (0,1), (1,0) and (0, -1), but the region is not exactly circular since it is formed by two parabolas. The graphs aren't vertical at (1,0) and (-1,0), for example, and a circle would be. The parabolas curve in such a way as to stay inside the circular region, so the region between the parabolas will have a bit less area than the circle.

The integrand (1-x^2) - (x^2-1) can be simplified to 2 - 2 x^2. An antiderivative would be 2x - 2/3 x^3. Evaluating this at -1 and 1 we obtain integral 8/3. The area of the region is 8/3 = 2.67 approx..

Note that the area of the circle described above would be pi = 3.14, approx., a bit bigger than the area of the region between the parabolas. *&*&

STUDENT ERROR: The graph is a circular region centered on the point (0,0)

INSTRUCTOR COMMENT:

The region is not exactly circular, (for example the graphs aren't vertical at (1,0) and (-1,0), for example), but it's fairly close to the circle. **

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Self-critique (if necessary):

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Self-critique Rating:

"

Self-critique (if necessary):

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Self-critique rating:

@& I suggest that you insert detailed self-critiques into this and into previously submitted Query documents, and resubmit them. I often can't tell what you do and do not understand. I need this information in order to provide feedback and, if necessary, assistance.

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