Assignment 13

course Mth 163

July 7, 2009 11pm*********************************************

Question: `q001. Note that this assignment has 12 questions

What does 2^5 mean?

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Your solution:

2*2*2*2*2

Confidence assessment rating: 3

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Given Solution:

2^5 stands for 2 raised to the fifth power; i.e., 2^5 = 2*2*2*2*2.

The result of this calculation is 2^5 = 32.

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Self-critique (if necessary):

Self-critique Rating:

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Question: `q002. What does 2^3 * 2^5 mean? Is the result of power of 2? If so, what power of 2 is it?

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Your solution:

(2*2*2) * (2*2*2*2*2) =256

This is 2 to the power of 8.

Confidence assessment rating: 3

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Given Solution:

2^3 * 2^5 means (2*2*2) * (2*2*2*2*2). This is the same as 2*2*2*2*2*2*2*2, or 2^8.

When we multiply this number out, we obtain 256.

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Self-critique (if necessary):

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Question: `q003. Why do we say that a^b * a^c = a^(b+c)?

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Your solution:

Because a is multiplied in both so it is just simplified.

Confidence assessment rating: 2

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Given Solution:

We saw in the preceding example that 2^3 * 2^5 stood for a product of three 2's, multiply by a product of five 2's. We saw also that the result was identical to a product of eight 2's. This was one instance of the general rule that when we multiply to different powers of the same number, the result is that number raised to the sum of the two powers.

One general way to state this rule is to let a stand for the number that is being raised to the different powers, and let b and c stand for those powers. Then we get the statement a^b * a^c = a^(b+c).

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Self-critique (if necessary):

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Question: `q004. What does (2^3)^5 mean?

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Your solution:

(2*2*2) *(2*2*2) *(2*2*2) *(2*2*2) *(2*2*2)

Confidence assessment rating: 3

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Given Solution:

Since 2^3 stands for 2*2*2, it follows that (2^3)^5 means (2^3)*(2^3)*(2^3)*(2^3)*(2^3) = (2*2*2)*(2*2*2)*(2*2*2)*(2*2*2)*(2*2*2) = 2*2*2*2*2*2*2*2*2*2*2*2*2*2*2 = 2^15.

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Self-critique (if necessary):

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Question: `q005. Why do we say that (a^b)^c = a^(b*c)?

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Your solution:

Because a has to be multiplied by b and c times. It is just a different arrangement of the equation.

Confidence assessment rating: 3

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Given Solution:

We saw in the last example how (2^3)^5 stands for the product of 5 quantities, each equal to the product of three 2's. We saw how this is equivalent to the product of fifteen 2's, and we saw how the fifteen was obtained by multiplying the exponents 3 and 5.

In the present question a^b stands for the quantity a multiplied by itself b times. (a^b)^c stands for the quantity a^b multiplied by itself c times, which is equivalent to multiplying a by itself b * c times. Thus we say that (a^b)^c = a^(b * c).

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Self-critique (if necessary):

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Question: `q006. According to the law a^b * a^c = a*(b+c), if we multiply 2^5 by 2^-2 what power of 2 should we get?

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Your solution:

2^5 * 2^-2= 2^(5+-2)= 2*2*2 or 2^3

Confidence assessment rating: 3

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Given Solution:

To according to the law, 2^5 * 2^-2 = 2^(5 + -2) = 2^(5-2) = 2^3.

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Self-critique (if necessary):

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Question: `q007. Since as we saw in the preceding question 2^5 * 2^-2 = 2^3, what therefore must be the value of 2^-2?

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Your solution:

I was going to say 4 or something but I had to look at the solution.

Confidence assessment rating: 1

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Given Solution:

One way of seeing this is to note that 2^5 = 32 and 2^3 = 8, so we have 32 * 2^-2 = 8. Dividing both sides by 32 we get 2^-2 = 8 / 32 = 1/4.

We can learn something important if we keep the calculation in powers of 2. If 2^5 * 2^-2 = 2^3, then dividing both sides of the equation by 2^5 we obtain 2^-2 = 2^3/2^5, which is equal to 1/2^2.

This shows us why 2^-2 = 1/2^2.

QUESTIONABLE STUDENT RESPONSE: .25

.25 is of course the value of 2^-2. However I'm not sure you've connected this with the fact that 2^5 * 2^-2 = 2^3, as was the intent of the question.

A key word in the given question is 'therefore', which asks you to connect your answer to the fact that 2^5 * 2^-2 = 2^3.

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Self-critique (if necessary):

I understand this now. I got confused but it’s clear to me now.

Self-critique Rating:

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Question: `q008. Why must we say that 2^-n = 1 / 2^n, where n stands for any counting number?

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Your solution:

Because n is a negative number, it will split whatever value n is.

Confidence assessment rating: 2

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Given Solution:

This is because for any number m, we have 2^m * 2^-n = 2^( m + -n) = 2^(m-n), and we also have 2^m * (1 / 2^n) = 2^m / 2^n = 2^(m-n). So whether we multiply 2^m by 2^-n or by 1 / 2^n we get the same result. This shows that 2^-n and 1 / 2^n are the same.

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Self-critique (if necessary):

I’m not sure if my solution was right or not.

It isn't clear what you meant by 'split', so I can't tell for sure whether you were thinking correctly.

However the key is that 2^-n * 2^n = 2^(-n + n) = 2^0 = 1, so that 2^-n must be 1 / 2^n.

Self-critique Rating:

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Question: `q009. According to the law a^b * a^c = a*(b+c), if we multiply 2^3 by 2^-3 what power of 2 should we get?

Since 2^-3 = 1 / 2^3, what number must we get when we multiply 2^3 by 2^-3?

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Your solution:

2^(3+-3)= This would equal 2^0

2^3 *(1/2 ^ 3)= 8*.125 = 1

Confidence assessment rating: 3

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Given Solution:

2^3 * 2^-3 = 2^(3 + -3) = 2^(3-3) = 2^0.

Since 2^-3 = 1 / 2^3 it follows that 2^3 * 2^-3 = 2^3 * ( 1 / 2^3) = 1.

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Self-critique (if necessary):

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Question: `q010. Continuing the last question, what therefore should be the value of 2^0?

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Your solution:

Since the alternate equation was equal to 1, I would assume 2^0 would also be 1.

Confidence assessment rating: 3

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Given Solution:

Since 2^3 * 2^-3 = 2^0 and also 2^3 * 2^-3 = 1 we see that 2^0 must be 1.

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Self-critique (if necessary):

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Question: `q011. How do we solve the equation x^3 = 12?

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Your solution:

∛12 = x

This equals 2.3

Confidence assessment rating: 2

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Given Solution:

We solve the equation by taking the 1/3 power of both sides:

(x^3)^(1/3) = 12^(1/3), then by the law (a^b)^c = a^(bc) we have

x^(3 * 1/3) = 12^(1/3), so that

x^1 = 12^(1/3) or just

x = 12^(1/3), which we can easily enough evaluate with a calculator. We obtain a result of approximately x = 2.29 .

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Self-critique (if necessary):

I used the wrong method but I understand!

Self-critique Rating:2

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Question: `q012. How do we solve the equation x^(5/2) = 44?

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Your solution:

x^(5/2 * 2/5)= 44^(2/5)

x^1= 44^2/5

x= 44^2/5

Confidence assessment rating: 3

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Given Solution:

If we take the 2/5 power of both sides we get

(x^(5/2))^(2/5) = 44^(2/5) or

x^(5/2 * 2/5) = 44^(2/5) or

x^1 = 44^(2/5) so that

x = 44^(2/5).

Evaluating by calculator you should obtain approximately x = 4.54.

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Self-critique (if necessary):

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