If your solution to 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.

 

 

 

 

 

011. `*   11

 

*   1.2.13 \ 5. Explain, step by step, how you solved the equation z^2 - z - 6 = 0 using factoring.

 

Your solution:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Confidence Assessment:

Given Solution:

* *  STUDENT SOLUTION WITH INSTRUCTOR COMMENT:

 

I factored this and came up with

 

(z + 2)(z - 3) = 0

 

Which broke down to

 

z + 2 = 0 and z - 3 = 0

 

This gave me the set {-2, 3}

 

-2 however, doesn't check out, but only 3 does, so the solution is:

 

z = 3

 

INSTRUCTOR COMMENT: It's good that you're checking out the solutions, because sometimes we get extraneous roots.  But note that -2 also checks: (-2)^2 - (-2) - 6 = 4 + 2 - 6 = 0. **

 

 

Self-critique (if necessary):

 

 

 

 

 

 

 

 

 

 

Self-critique Rating:

Question: *   1.2.14 (was 1.3.6). Explain how you solved the equation v^2+7v+6=0 by factoring.

 

Your solution:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Confidence Assessment:

Given Solution:

* * STUDENT SOLUTION:

 

v^2+7v+6=0. This factors into

 

(v + 1) (v + 6) = 0, which has solutions

 

v + 1 = 0 and v + 6 = 0, giving us

 

v = {-1, -6}

 

 

 

Self-critique (if necessary):

 

 

 

 

 

 

 

 

 

 

Self-critique Rating:

Question: *   1.2.20 (was 1.3.12). Explain how you solved the equation x(x+4)=12 by factoring.

 

Your solution:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Confidence Assessment:

Given Solution:

* *  Starting with

 

x(x+4)=12 apply the Distributive Law to the left-hand side:

 

x^2 + 4x = 12 add -12 to both sides:

 

x^2 + 4x -12 = 0 factor:

 

(x - 2)(x + 6) = 0 apply the zero property:

 

(x - 2) = 0 or (x + 6) = 0 so that

 

x = {2 , -6} **

 

Self-critique (if necessary):

 

 

 

 

 

 

 

 

 

 

Self-critique Rating:

Question: *   1.2.26 \ 38 (was 1.3.18). Explain how you solved the equation x + 12/x = 7 by factoring.

 

Your solution:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Confidence Assessment:

Given Solution:

* *  Starting with

 

x + 12/x = 7 multiply both sides by the denominator x:

 

x^2 + 12 = 7 x add -7x to both sides:

 

x^2 -7x + 12 = 0 factor:

 

(x - 3)(x - 4) = 0 apply the zero property

 

x-3 = 0 or x-4 = 0 so that

 

x = {3 , 4} **

 

 

 

Self-critique (if necessary):

 

 

 

 

 

 

 

 

 

 

Self-critique Rating:

Question: *   1.2.32 (was 1.3.24). Explain how you solved the equation (x+2)^2 = 1 by the square root method.

 

Your solution:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Confidence Assessment:

Given Solution:

* *  (x + 2)^2 = 1 so that

 

x + 2 = ± sqrt(1) giving us

 

x + 2 = 1 or x + 2 = -1 so that

 

x = {-1, -3} **

 

 

Self-critique (if necessary):

 

 

 

 

 

 

 

 

 

 

Self-critique Rating:

Question: *   1.2.38 (was 1.3.36). Explain how you solved the equation x^2 + 2/3 x - 1/3 = 0 by completing the square.

 

Your solution:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Confidence Assessment:

Given Solution:

* *  x^2 + 2/3x - 1/3 = 0. Multiply both sides by the common denominator 3 to get

 

3 x^2 + 2 x - 1 = 0. Factor to get

 

(3x - 1) ( x + 1) = 0. Apply the zero property to get

 

3x - 1 = 0 or x + 1 = 0 so that

 

x = 1/3 or x = -1.

 

STUDENT QUESTION:

 

 The only thing that confuses me is the 1/3. Is that because of the 3x?

INSTRUCTOR RESPONSE:

 

You got the equation

(3x - 1) ( x + 1) = 0.

The product of two numbers can be zero only if one of the numbers is zero.

So (3x - 1) ( x + 1) = 0 means that

3x - 1 = 0 or x + 1 = 0. You left out this step in your solution.

x + 1 = 0 is an equation with solution x = -1

Thus the solution to our original equation is

x = 1/3 or x = -1.
 

 

Self-critique (if necessary):

 

 

 

 

 

 

 

 

 

 

Self-critique Rating:

 

Question: *   1.2.44 \ 52 (was 1.3.42). Explain how you solved the equation x^2 + 6x + 1 = 0 using the quadratic formula.

 

Your solution:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Confidence Assessment:

Given Solution:

* *  Starting with

 

x^2 + 6x + 1 = 0

 

we identify our equation as a quadratic equation, having the form a x^2 + b x + c = 0 with a = 1, b = 6 and c = 1.

 

We plug values into quadratic formula to get

 

x = [-6 ± sqrt(6^2 - 4 * 1 * 1) ] / 2 *1

 

x = [ -6 ± sqrt(36 - 4) / 2

 

x = { -6 ± sqrt (32) ] / 2

 

36 - 4 = 32, so x has 2 real solutions,

 

x = [-6 + sqrt(32) ] / 2  and

x =  [-6 - sqrt(32) ] / 2

 

Our solution set is therefore

 

{ [-6 + sqrt(32) ] / 2 , [-6 - sqrt(32) ] / 2 }

 

 

Now sqrt(32) simplifies to sqrt(16) * sqrt(2) = 4 sqrt(2) so this solution set can be written

 

{ [-6 + 4 sqrt(2) ] / 2 , [-6 - 4 sqrt(2) ] / 2 },

 

and this can be simplified by dividing numerators by 2:

 

{ -3 + 2 sqrt(2), -3 - 2 sqrt(2) }. **

 

 

 

Self-critique (if necessary):

 

 

 

 

 

 

 

 

 

 

Self-critique Rating:

Question: *   1.2.69 \ 1.2.78 \ 72 (was 1.3.66). Explain how you solved the equation pi x^2 + 15 sqrt(2) x + 20 = 0 using the quadratic formula and your calculator.

 

Your solution:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Confidence Assessment:

Given Solution:

* *  Applying the quadratic formula with a = pi, b = 15 sqrt(2) and c = 20 we get

 

x = [ (-15sqrt(2)) ± sqrt (  (-15sqrt(2))^2 -4(pi)(20) ) ] / ( 2 pi ).

 

The discriminant (-15sqrt(2))^2 - 4(pi)(20) = 225 * 2 - 80 pi = 450 - 80 pi = 198.68 approx., so there are 2 unequal real solutions.

 

Our expression is therefore

 

x = [ (-15sqrt(2)) ± sqrt(198.68)] / ( 2 pi ).

 

Evaluating with a calculator we get

 

x = { -5.62, -1.13 }.

 

 

 

DER**

 

 

 

Self-critique (if necessary):

 

 

 

 

 

 

 

 

 

 

Self-critique Rating:

Question: *   1.2.106 \ 98 (was 1.3.90). Explain how you set up and solved an equation for the problem. Include your equation and the reasoning you used to develop the equation. Problem (note that this statement is for instructor reference; the full statement was in your text) box vol 4 ft^3 by cutting 1 ft sq from corners of rectangle the L/W = 2/1.

 

Your solution:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Confidence Assessment:

Given Solution:

* *  Using x for the length of the shorter side of the rectangle the 2/1 ratio tells us that the length is 2x.

 

If we cut a 1 ft square from each corner and fold the 'tabs' up to make a rectangular box we see that the 'tabs' are each 2 ft shorter than the sides of the sheet. So the sides of the box will have lengths x - 2 and 2x - 2, with measurements in feet. The box so formed will have height 1 so its volume will be

 

volume = ht * width * length = 1(x - 2) ( 2x - 2).

 

If the volume is to be 4 we get the equation

 

1(x - 2) ( 2x - 2) = 4.

 

Applying the distributive law to the left-hand side we get

 

2x^2 - 6x + 4 = 4

 

Divided both sides by 2 we get

 

x^2 - 3x +2 = 2.

We solve by factoring.  x^2 - 3x + 2 = (x - 2) ( x - 1) so we have

 

(x - 2) (x - 1) = 2. Subtract 2 from both sides to get

 

x^2 - 3 x = 0 the factor to get

 

x(x-3) = 0. We conclude that

 

x = 0 or x = 3.

 

We check these results to see if they both make sense and find that x = 0 does not form a box, but x = 3 does.

 

 

x stands for the shorter side of the rectangle, which is therefore 3.  The longer side is double the shorter, or 6.

 

Thus to make the box:

 

We take our 3 x 6 rectangle, cut out 1 ft corners and fold it up, giving us a box with dimensions 1 ft x 1 ft x 4 ft. 

 

This box has volume 4 cubic feet, confirming our solution to the problem.

FURTHER BREAKDOWN OF THE PROBLEM INTO A SEQUENCE OF QUESTIONS

 

  1. Sketch a rectangle.

  2. Now take a square 'bite' out of each corner of the rectangle.

  3. This gives you a 'tab' on each side, running along most of the length or width of that side, but shorter because of the cut-out squares.

  4. If you fold up these 'tabs' you will form a box, open at the top.

  5. Now if the squares you cut out are 1-foot squares, and the width of the original rectangle is x, what is the width of the box?

  6. What was the original length of your original rectangle, and what is the length of your box?

  7. What there fore are the three dimensions of the box?

  8. In terms of x, what is its volume?

 

Self-critique (if necessary):

 

 

 

 

 

 

 

 

 

 

Self-critique Rating:

Question: *   1/2/100 / 1.2.108 \ 100 (was 1.3.96). Explain how you set up and solved an equation for the problem. Include your equation and the reasoning you used to develop the equation. Problem (note that this statement is for instructor reference; the full statement was in your text) s = -4.9 t^2 + 20 t; when 15 m high, when strike ground, when is ht 100 m.

 

 

 

Your solution:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Confidence Assessment:

Given Solution:

* *  To find the clock time at which the object is 15 m off the ground we set the height s equal to 15 to get the equation

 

-4.9t^2 + 20t = 15

 

Subtracting 15 from both sides we get

 

-4.9t^2 +20t - 15 = 0

 

so that

 

t = { -20 ± sqrt [20^2 - 4(-4.9)(-15) ] } / (2(-4.9))

 

Numerically these simplify to t = .99 and t = 3.09.

 

Interpretation:

 

 

To find when the object strikes the ground we set s = 0 to get the equation

 

-4.9t^2 + 20t = 0

 

which we solve to get

 

t = [ -20 ± sqrt [20^2 - 4(-4.9)(0)] ] / (2(-4.9))

 

This simplifies to

 

t = [ -20 +-sqrt(20^2) ] / (2 * -4.9) = [-20 +- 20 ] / (-9.8).

 

The solutions simplify to t = 0 and t = 4.1 approx.

 

Interpretation:

 

The object is at the ground at t = 0, when it starts up, and at t = 4.1 seconds, when it again strikes the ground.

 

To find when the altitude is 100 we set s = 100 to get

 

-4.9t^2 + 20t = 100.

 

Subtracting 100 from both sides we obtain

 

-4.9t^2 +20t - 100 = 0

 

which we solve using the quadratic formula. We get

 

t = [ -20 ± sqrt (20^2 - 4(-4.9)(-100)) ] / (2(-4.9))

 

The discriminant is 20^2 - 4 * -4.9 * -100, which turns out to be negative so we do not obtain a solution.

 

Interpretation: 

 

We conclude that this object will not rise 100 ft. **

 

STUDENT QUESTION

 

I was lost on this question and even reading the solution, Im still confused about it. Do you have any suggestions on how to look at it in a different way???



INSTRUCTOR RESPONSE


s = -4.9 t^2 + 20 t

means that if you plug in a value of t, you get the height, which is represented by the variable s.

Also if you want to find the value of t that gives you a certain height, you plug in that height for s and solve the equation for t.

The first question asks you to find when the height is 15 meters.

So you plug in 15 for s.

What equation do you get?

You get the equation 15 = -4.9 t^2 + 20 t.

Now you solve the equation for t.

How do you do that?


The equation is quadratic, since it contains both t^2 and t.

The standard form for a quadratic equation is

a t^2 + b t + c = 0

In this form you can try to factor the left-hand side. If this is possible you can then apply the zero property, as you've done in some of the preceding problems.

If you can't figure out how to factor the equation (and in real-world problems you usually can't), you can use the quadratic formula.

In this case you rearrange the equation

15 = -4.9 t^2 + 20 t

to the form

-4.9 t^2 + 20 t - 15 = 0

and pretty quickly realize that you won't be able to factor it. So you use the quadratic formula, as shown in the given solution.
 

STUDENT QUESTION

 

This is the part I am confused about. How did it go from the top equation to the numbers .99 and 3.09?

INSTRUCTOR RESPONSE


To evaluate

{ -20 ± sqrt [20^2 - 4(-4.9)(-15) ] } / (2(-4.9))

follow the order of operations:

First evaluate the expression in braces:

{ -20 ± sqrt [20^2 - 4(-4.9)(-15) ] }
= -20 ± sqrt [20^2 - 4(-4.9)(-15) ]

Start with the expression in brackets, which is

20^2 - 4(-4.9)(-15)

Find 20^2, multiply 4(-4.9)(-15), and subtract the second result from the first.

Then take the square root of the result, giving you the value of

sqrt(20^2 - 4(-4.9)(-15)).

Now evaluate

-20 ± sqrt [20^2 - 4(-4.9)(-15) ]

You get two results, one based on the + of the ± and the other on the -:

First add the value of the square root to -20.

Then subtract the value of the square root from -20.

This completes evaluation of the quantity in braces.


Now evaluate the denominator 2 ( -4.9), which you multiply to get -9.8.


Divide the first value of the numerator by -9.8 to get .99.

Divide the second value of the numerator by -9.8 to get 3.09.





 

 

Self-critique (if necessary):

 

 

 

 

 

 

 

 

 

 

Self-critique Rating:

Question: *   Add comments on any surprises or insights you experienced as a result of this assignment.