6

course Mth 163

I have alot of trouble with this assignment. I'm going to go back and review. I wanted to send you what I have done so the work isn't lost. Sorry for the inconvenence.

query problem 2. ave rates at midpoint timeswhat is the average rate of depth change for the 1-second time interval centered at the 50 sec midpoint?

Your work has been received. Please scroll through the document to see any inserted notes (inserted at the appropriate place in the document, in boldface) and a note at the end. The note at the end of the file will confirm that the file has been reviewed; be sure to read that note. If there is no note at the end, notify the instructor through the Submit Work form, and include the date of the posting to your access page.

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assignment #006

006. `query 6

Precalculus I

03-21-2007

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17:13:19

Query 4 basic function families

What are the four basic functions?

What are the generalized forms of the four basic functions?

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RESPONSE -->

Linear, quadratic, general exponential, and power funtion

Linear y=f(x)= mx+b (slope-intercept form)

Quadratic y=f(x)=ax^2+bx+c

Exponential y=f(x)=2^x

Power function y=f(x)=x^p

confidence assessment: 2

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17:13:40

** STUDENT RESPONSE:

Linear is y=mx+b

Quadratic is y=ax^2 + bx +c

Exponential is y= A*2^ (kx)+c

Power = A (x-h)^p+c

INSTRUCTOR COMMENTS:

These are the generalized forms. The basic functions are y = x, y = x^2, y = 2^x and y = x^p. **

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RESPONSE -->

ok

self critique assessment: 3

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17:27:25

For a function f(x), what is the significance of the function A f(x-h) + k and how does its graph compare to that of f(x)?

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RESPONSE -->

A f(x-h) +k is the graph of f(x) shifted to the right h units, vertically shifted up k units and either vertically shrunken (01) by a factor of A

confidence assessment: 2

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17:28:24

** STUDENT RESPONSE: A designates the x strectch factor while h affects a y shift & k affects an x shift

INSTRUCTOR COMMENTS:

k is the y shift for a simple enough reason -- if you add k to the y value it raises the graph by k units.

h is the x shift. The reason isn't quite as simple, but not that hard to understand. It's because when x is replaced by x - h the y values on the table shift 'forward' by h units.

A is a multiplier. When all y values are multiplied by A that moves them all A times as far from the x axis, which is what causes the stretch.

Thus A f(x-h) + k is obtained from f(x) by vertical stretch A, horizontal shift h and vertical shift k.

The two aren't the same, but of course they're closely related. **

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RESPONSE -->

ok

self critique assessment: 2

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17:29:48

query introduction to rates and slopes, problem 1 ave vel for function depth(t) = .02t^2 - 5t + 150

give the average rate of depth change from t = 20 to t = 40

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RESPONSE -->

I don't understand what your asking. What is ""ave vel""?

confidence assessment: 3

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17:32:13

** depth(20) = .02(20^2) - 5(20) + 150 = 58

depth(40) = .02(40^2) - 5(40) + 150 = -18

change in depth = depth(40) - depth(20) = -18 - 58 = -76

change in clock time = 40 - 20 = 20.

Ave rate of depth change = change in depth / change in clock time = -76 / 20 = -3.8 **

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RESPONSE -->

I understand this process, but the question still doesn't make sense to me.

self critique assessment: 3

You shouldn't be trying to read the problems from the abbreviated statements given in the Query. Problems are stated in the worksheets.

This particular problem is the first under 'Exercises' in the worksheet Introduction to Rates and Slopes, from Assignment 6. A full statement of the problem is

1. For the depth vs. time function depth(t) = .02t^2 - 5t + 150, determine the average rate of change of the depth for each of the following time intervals:

t = 0 to t = 20

t = 20 to t = 40

t = 40 to t = 60

t = 60 to t = 80

t = 80 to t = 100

Sketch a graph depicting your calculations.

Is there a pattern to the depth change rates you have obtained?

Having worked the problem on the worksheet, it is expected that you will be able to answer the question 'give the average rate of depth change from t = 20 to t = 40', or if you made an error, to recognize and self-critique the solution to this question.

Incidentally the term 'ave vel' means 'average velocity'; you wouldn't necessarily know that but to answer the question it's not necessary to know that.

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17:33:22

What is the average rate of depth change from t = 60 to t = 80?

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RESPONSE -->

Obviously this pertains to the previous question that I didn't understand. Sorry.

confidence assessment: 3

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17:34:45

** depth(60) = .02(60^2) - 5(60) + 150 = -78

depth(80) = .02(80^2) - 5(80) + 150 = -122

change in depth = depth(80) - depth(60) = -122 - (-78) = -44

change in clock time = 40 - 20 = 20.

Ave rate of depth change = change in depth / change in clock time = -44 / 20 = -2.2 **

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RESPONSE -->

I see that you take the slope of a function from one point the next point in time. The average is a linear change.

self critique assessment: 2

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17:47:51

describe your graph of y = .02t^2 - 5t + 150

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RESPONSE -->

Upward facing parabola with a vertex at (125,-162 1/2)

confidence assessment: 1

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17:48:56

** The graph is a parabola.

y = .02t^2 - 5t + 150 has vertex at x = -b / (2a) = -(-5) / (2 * .02) = 125, at which point y = .02 (125^2) - 5(125) + 150 = -162.5.

The graph opens upward, intercepting the x axis at about t = 35 and t = 215.

Up to t = 125 the graph is decreasing at a decreasing rate. That is, it's decreasing but the slopes, which are negative, are increasing toward 0.**

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RESPONSE -->

sorry forgot to include where the graph intercepts at the x axis

self critique assessment: 2

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17:51:50

describe the pattern to the depth change rates

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RESPONSE -->

Apparently I've missed something because I'm not sure what your asking.

confidence assessment: 3

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17:53:55

** Rates are -3.8, -3 and -2.2 for the three intervals (20,40), (40,60) and (60,80).

For each interval of `dt = 20 the rate changes by +.8. **

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RESPONSE -->

I'm going to go back and review because I've missed something.

self critique assessment: 3

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See my notes.

Did you work the exercises as assigned on the worksheet?