Assign 14

course Mth 158

Okay! This program is crazy. Just kidding but sorry for the last problem, I don't know what happened.Thanks

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assignment #014

014. `query 14

College Algebra

02-21-2007

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20:19:52

**** query 1.5.34 (was 1.5.24). How did you write the interval [0, 1) using an inequality with x? Describe your illustration using the number line.

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RESPONSE -->

[0,1) consists of all numbers x for which 0< or = x<1

using the half-open interval [a,b), a

confidence assessment: 3

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20:20:22

** My notes here show the half-closed interval [0, 1).

When sketching the graph you would use a filled dot at x = 0 and an unfilled dot at x = 1, and you would fill in the line from x = 0 to x = 1. **

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RESPONSE -->

Okay!

self critique assessment: 2

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20:22:03

1.5.40 (was 1.5.30). How did you fill in the blank for 'if x < -4 then x + 4 ____ 0'?

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RESPONSE -->

if x< -4, then x+4<0

confidence assessment: 2

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20:22:27

** if x<-4 then x cannot be -4 and x+4 < 0.

Algebraically, adding 4 to both sides of x < -4 gives us x + 4 < 0. **

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RESPONSE -->

yep

self critique assessment: 2

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20:23:34

1.5.46 (was 1.5.36). How did you fill in the blank for 'if x > -2 then -4x ____ 8'?

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RESPONSE -->

if x> -2, then -4x > 8

multiply both sides by -4

confidence assessment: 2

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20:24:20

**if x> -2 then if we multiply both sides by -4 we get

-4x <8.

Recall that the inequality sign has to reverse if you multiply or divide by a negative quantity. **

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RESPONSE -->

ooops...I didn't reverse but now I know.

self critique assessment: 2

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20:29:17

1.5.58 (was 1.5.48). Explain how you solved the inquality 2x + 5 >= 1.

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RESPONSE -->

2x+5>=1

2x+5-5>=1-5 subtract both sides by 5

2x>= -4

2x/2>=-4/2 divide both sides by 2

x>= -2

{x|x>= -2}

[-2,infinity)

confidence assessment: 2

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20:29:45

** Starting with

2x+5>= 1 we add -5 to both sides to get

2x>= -4, the divide both sides by 2 to get the solution

x >= -2. **

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RESPONSE -->

whooah! so I am getting the hang of this.

self critique assessment: 2

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20:33:41

1.5.64 (was 1.5.54). Explain how you solved the inquality 8 - 4(2-x) <= 2x.

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RESPONSE -->

8 - 4(2-x)<=2x

8 - 8 - 4x<=2x

-4x<=2x

-4x-2x<=2x-2x

-6x<=0

-6x/-6<=0/-6

reverse the inequality when you multiply or divide by a negative

x= - 0/6

confidence assessment: 2

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20:40:29

1.5.76 (was 1.5.66). Explain how you solved the inquality 0 < 1 - 1/3 x < 1.

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RESPONSE -->

ooops. I worked that a little wrong should have changed my - to a plus.

0<1 - 1/3x<1

(3)0<(1-1/3x)3<1(3) multiply by 3

0<3-x<3

0-3<3-x-3<3-3 subtract by 3

-3<-x<0 divide by -1

3>x>0

{x|3>x>0} or (0,3)

confidence assessment: 2

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20:41:11

** Starting with

0<1- 1/3x<1 we can separate this into two inequalities, both of which must hold:

0< 1- 1/3x and 1- 1/3x < 1. Subtracting 1 from both sides we get

-1< -1/3x and -1/3x < 0. We solve these inequalitites separately:

-1 < -1/3 x can be multiplied by -3 to get 3 > x (multiplication by the negative reverses the direction of the inequality)

-1/3 x < 0 can be multiplied by -3 to get x > 0.

So our inequality can be written 3 > x > 0. This is not incorrect but we usually write such inequalities from left to right, as they would be seen on a number line. The same inequality is expressed as

0 < x < 3. **

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RESPONSE -->

Okay so I got it right but didn't flip the expression.

self critique assessment: 2

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20:45:22

1.5.94 (was 1.5.84). Explain how you found a and b for the conditions 'if -3 < x < 3 then a < 1 - 2x < b.

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RESPONSE -->

if - 3

ok so maybe I don't get it.

confidence assessment: 0

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20:48:05

** Adding 1 to each expression gives us

1 + 6 > 1 - 2x > 1 - 6, which we simplify to get

7 > 1 - 2x > -5. Writing in the more traditional 'left-toright' order:

-5 < 1 - 2x < 7. **

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RESPONSE -->

So to get the 6>1-2x>-6, you need to multiply by 2??

I will work on this kinda of problem.

self critique assessment: 2

Your inequality is originally expressed in terms of x. To get -2x you multiply by -2. So if you multiply the inequality by -2 you will get the inequality for -2x.

Then add 1 to all expressions and you have your inequality for 1 - 2x.

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20:51:38

1.5.106 (was 1.5.96). Explain how you set up and solved an inequality for the problem. Include your inequality and the reasoning you used to develop the inequality. Problem (note that this statement is for instructor reference; the full statement was in your text) commision $25 + 40% of excess over owner cost; range is $70 to $300 over owner cost. What is range of commission on a sale?

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RESPONSE -->

I really have a hard time with problem solving.

confidence assessment: 0

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20:58:21

** If x = owner cost then

70 < x < 300.

.40 * owner cost is then in the range

.40 * 70 < .40 x < .40 * 300 and $25 + 40% of owner cost is in the range

25 + .40 * 70 < 25 + .40 x < 25 + .40 * 300 or

25 + 28 < 25 + .40 x < 25 + 120 or

53 < 25 + .40 x < 145. **

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RESPONSE -->

Ok to get this i need to find an x out of the problem, like in this one x = owner cost, then I need to think of what I am working on like in this one inequalities, given 70

self critique assessment: 2

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21:01:22

1.5.112. Why does the inequality x^2 + 1 < -5 have no solution?

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RESPONSE -->

Be cause you can't sqrt a negative number.

confidence assessment: 2

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assignment #014

014. `query 14

College Algebra

02-21-2007

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21:04:41

STUDENT SOLUTION: x^2 +1 < -5

x^2 < -4

x < sqrt -4

can't take the sqrt of a negative number

INSTRUCTOR COMMENT: Good.

Alternative: As soon as you got to the step x^2 < -4 you could have stated that there is no such x, since a square can't be negative. **

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RESPONSE -->

ok thats what I got but it kicked me out of the program. who knows!

self critique assessment: 2

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Good work. See my notes.