assignment 1

course Mth 164

I got alot of these wrong but I'm getting it

assignment #001

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.

001. Radian measure and the unit circle.

Precalculus II

09-26-2007

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07:53:18

Previous Assignments:

Be sure you have completed all Preliminary Assignments as instructed on under the Assts link on the homepage at 164.106.222.236. These assignments include the q_a_orientation, and the three sets Initial Problems, Describing Graphs and Typewriter Notation from the q_a_init_pbs program. Links and explanations are included on the Assignments Page.

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RESPONSE -->

ok

self critique assessment: 3

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07:58:54

`q001. Note that there are 10 activities in this assignment.

Figure 37 (located under the Figures link on the Assignments page under Assignment 0) depicts a circle of radius 1 centered at the origin of a x y coordinate system. Imagine the we have 2 ants, one red and one black. Both start out moving at the same speed from the point for the positive x-axis beats the circle. The red ant crawls along the arc of the circle in the counterclockwise direction, and black ant crawls along the x-axis toward the origin. The ants proceed until the black ant reaches the origin. Both ants will have crawled the same distance, the black ant along a straight line and the red ant along an arc of the circle.

At that instant the red ant will have traveled a distance equal to 1 radius of the circle, and we say that the red ant has completed 1 radian of arc. Which of the indicated points on the circle will correspond to a 1 radian arc? Note that we have indicated points a, b, c, d.

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RESPONSE -->

The point would be B because the wat the circle is divided up it couldnt be any ov the others

confidence assessment: 2

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07:59:40

We see visually that the point a lies at an arc distance less than the radius of the circle. We also see that the point c lies at an arc distance that is clearly greater than the radius of the circle. The only possible candidate for a 1 radian angle, which must lie at an arc distance equal to one radius, is therefore point b.

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RESPONSE -->

this is the answer I got

self critique assessment: 3

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08:06:18

`q002. If the first ant moves at a constant speed, moving through 1 radian every second, then approximately how long, to the nearest second, do you think it will take for the ant to move along the arc to the point where the circle meets the negative x-axis?

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RESPONSE -->

it will take the ant 18 seconds to get to the negative x axis

confidence assessment: 2

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08:07:09

Visual examination, perhaps accompanied by a quick sketch, shows that it takes approximately 3 arcs each of one radian to get from the positive x-axis to the negative x-axis when moving along the arc of the circle.

In figure 37 the points b, c and d lie at approximately 1, 2 and 3 radians. Remember that each radian corresponds to an arc distance equal to the radius of the circle.

At 1 radian / second it will take about 3 seconds to move the approximately 3 radians to the negative x axis.

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RESPONSE -->

I got this wrong because I look at the radians differently

self critique assessment: 2

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08:07:42

`q003. If the ant traveled at 1/2 radian per second, then after 1 second would its angular position be indicated by point a, point b, point c or point d in Figure 37?

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RESPONSE -->

confidence assessment:

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08:08:07

`q003. If the ant traveled at 1/2 radian per second, then after 1 second would its angular position be indicated by point a, point b, point c or point d in Figure 37?

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RESPONSE -->

it would sdtill be at point b

confidence assessment: 2

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08:08:45

After 1 second the angular position would be 1/2 radian, which would correspond to point a.

Note that after 2 seconds the angular position would be 1 radian, corresponding to point b, and after three seconds the angular position would be 3 * 1/2 radian = 3/2 radian and the ant would be at position c.

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RESPONSE -->

I miss this one because I counted them differently

self critique assessment: 2

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08:09:58

`q004. How far will the ant travel in the process of completing 1 trip around the circle, starting and ending at the initial point where the circle meets the positive x-axis.

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RESPONSE -->

The ant will travel 8 radians

confidence assessment: 1

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08:10:40

The circumference of the circle is 2 pi r, where r is the radius of the circle. This is the distance traveled by the ant.

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RESPONSE -->

I knew this one but forgot about the 2pi r

self critique assessment: 1

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08:11:37

`q005. As we just saw the distance around the circle is its circumference 2 pi r, where r is the radius. Through how many radians would the ant travel from the initial point, where the circle meets the positive x-axis, if the motion was in the counterclockwise direction and ended at the original point after having completed one trip around the circle.

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RESPONSE -->

the ant would travel 8 raidians

confidence assessment: 1

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08:12:42

An arc displacement of r corresponds to an arc distance of 1 radian on the circle. Arc distances of 2, 3, 4, ... time the radius would correspond to 2, 3, 4, ... radians of arc. That is, arc distance of r, 2r, 3r, 4r, ... correspond to 1, 2, 3, 4, ... radians of arc.

We understand by these examples that if we divide the arc distance by the radius, we will get the number of radians of angular distance.

The arc distance around the circle is 2 pi r, which therefore corresponds to 2 pi r / r = 2 pi radians.

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RESPONSE -->

Is 2pi r the same as 8 radians

self critique assessment: 1

It's only 2 pi radians of angle around the circle. 2 pi is about 2 * 3.14 = 6.28.

8 radians would go all the way around the circle, then another 1.72 radians.

The arc distance on the circle corresponding to each radian is equal to the radius r. You travel distance r along the circle for each radian of angle.

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08:15:02

`q006. The unit circle is a circle of radius 1 centered at the origin. What are the coordinates of the points where the unit circle meets the positive x-axis, the positive y axis, the negative x-axis and the negative y axis?

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RESPONSE -->

The point would be (0,0)

confidence assessment: 0

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08:15:54

The unit circle has radius 1 and is centered at the origin, so the circle meets the positive x-axis 1 unit from the origin at (x, y) = (1,0). Similarly the circle meets the positive y-axis at the 'top' of the circle, 1 unit from the origin at (x, y) = (0,1); the circle meets the negative x-axis at (-1, 0); and the circle meets the negative y-axis at (0,-1).

Figure 84 shows these points on the unit circle. Note that in this figure the small dots are located at increments of .1 unit in the x and y directions.

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RESPONSE -->

I should have know aboout the points of 1

self critique assessment: 1

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08:16:36

`q007. Without looking at Figure 84, sketch a picture of the unit circle, complete with labeled points where the circle meets the x and y axes. Indicate the arc from the standard initial point, where the circle meets the x-axis, to the point where the circle meets the positive y axis. Describe your sketch.

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RESPONSE -->

I'm unsure how to sketch the answer

confidence assessment: 0

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08:17:03

Your sketch should show the x and y axes and a circle of radius 1, with the points (1,0), (0, 1), (-1, 0) and (0, -1) where the circle meets the coordinate axes labeled. The arc will run along the first quadrant of the circle from (1,0) to (0,1). Your figure should match figure 84.

You should be able to quickly draw this picture any time you need it.

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RESPONSE -->

I need to figure out how to do that

self critique assessment: 0

Can you draw figure 84? If so, then practice drawing it, with all details, from memory.

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08:18:24

`q008. How many radians of angular displacement correspond to the arc displacement from the standard initial point, where the circle meets the x-axis, to the point where the circle meets the positive y axis?

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RESPONSE -->

the answer is 9 radians

confidence assessment: 0

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08:19:45

The trip around the entire circle, which corresponds to an angular displacement of 2 pi radians, corresponds to a trip from the initial point to the point where the circle meets the positive y-axis (i.e., the point (0,1)), then from this point to the point where the circle meets the negative x-axis (i.e., the point (-1,0)), then from this point to the point where the circle meets the negative y-axis (i.e., the point (0,-1)), then from this point back to the point where the circle meets the positive x-axis (i.e., the point (1,0)).

Because of the symmetry of the circle, the arc corresponding to each of these displacements is the same. The arc from (1,0) to (0,1) is 1/4 of the 2 pi radian angular displacement around the entire circle, so its angular displacement is 2 pi/4 = pi/2 radians.

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RESPONSE -->

I forgot about pi I'm going to study up on this

self critique assessment: 1

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08:25:23

`q009. We have just seen that the angular position of the (1,0) point is 0 and the angular position of the (0,1) point is pi/2. What are the angular positions of the (-1,0) and (0,-1) points?

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RESPONSE -->

(-1,0) is going to be 0 and (0,-1) pi/-2

confidence assessment: 1

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08:26:24

These points are reached after successive angular displacements of pi/2. The (-1,0) point is reached from the pi/2 position by an additional angular displacement of pi/2, which puts it at angular position pi.

The (0,-1) point is reached after another angular displacement of pi/2, which puts it at pi + pi/2 = 2 pi/2 + pi/2 = 3 pi/2.

Note that still another angular displacement of pi/2 puts us back at the initial point, whose angular position is 0. This shows that the initial point has angular position 0, or angular position 3 pi/2 + pi/2 = 4 pi/2 = 2 pi, consistent with what we already know.

You should label your picture with these angular positions pi/2, pi, 3 pi/2 and 2 pi specified at the appropriate points.

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RESPONSE -->

I need to understand more about pi around the circle

self critique assessment: 1

pi is the ratio of circumference to diameter of a circle

So the circumference of the circle is pi * diameter.

Diameter is 2 * radius.

So the circumference is pi * 2 * radius, or in abbreviated form 2 pi r.

Each arc distance of r corresponds to an angle of 1 radian.

So there are 2 pi radians in the angle which 'covers' the entire arc of the circle.

Thus 2 pi radians is the same as 360 degrees.

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08:26:54

`q010. What is the angular displacement from the standard initial point of the point halfway along the arc of the circle from (1,0) to (0,1)? Note that you should begin with a sketch of the circle and of the arc specified here.

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RESPONSE -->

I dont know how to sketch

confidence assessment: 0

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08:27:32

(1,0) is the point at which the circle meets the positive x-axis and (0,1) is the point at which the circle meets the positive y-axis. The trip along the arc of the circle from (1,0) to (0,1) will move along the first-quadrant arc from angular position 0 to angular position pi/2. Halfway along this arc, the angular position will be 1/2 * pi/2 = pi/4.

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RESPONSE -->

If I knew how to sketch I might have done better on this one

self critique assessment: 0

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08:28:06

`q011. What will be the angular positions of the arc points halfway between the (0,1) and (-1,0) points of the circle?

What will be the angular positions of the arc points halfway between the (-1,0) and (0,-1) points of the circle?

What will be the angular positions of the arc points halfway between the (0,-1) and (1,0) points of the circle?

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RESPONSE -->

confidence assessment: 0

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You need to review the figures in this exercise, and you need to be able to sketch them in detail, without referring to a previous sketch or to the figure.

Practice doing that, let me know if you have any questions (just put your questions into the box in the Submit Work Form), then you should redo this assignment and resubmit it. You have to get these pictures right in order to make sense of what follows.