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Mathematics 21 Online
OpenStudy (katecc379):

hwlp

OpenStudy (katecc379):

OpenStudy (mathmale):

As you can easily see, you're working with 2 different bases here. Note that base 100 is the same as base 10^2. I would change these 2 equations to exponential form. The first one becomes\[10^{\log_{10}50 }=10^{1.699}\]

OpenStudy (mathmale):

How would you simplify the left side?

OpenStudy (mathmale):

Can you now use this info to rewrite \[\log_{100}50? \]

OpenStudy (katecc379):

log50/2?

OpenStudy (mathmale):

Think:\[\log_{100}50=\log_{10^2}50 \]

OpenStudy (katecc379):

im so confused im sorry

OpenStudy (mathmale):

I would write\[\log_{100}50=x\] and then re-write this in exponential form. Are you able to do that?

OpenStudy (katecc379):

log100^x=50?

OpenStudy (mathmale):

Unfortunately, no. Your base here is 100, or 10^2. "log" does not belong in the desired "exponential form" equation. Mind thinking this over and then trying again?

OpenStudy (katecc379):

100^x=50

OpenStudy (katecc379):

sorry didnt mean to put the log

OpenStudy (mathmale):

if 100^x=50, how would you find the value of x?

OpenStudy (mathmale):

Note that y ou are given that log 50=1.699. You need to use that info to find the log to the base 100 of 50.

OpenStudy (mathmale):

Time to stop for a sec. What part of this procedure is clear to you and what part is not?

OpenStudy (katecc379):

i understand how its in exponential and i understand the value of x i just dont know how to find the new value

OpenStudy (mathmale):

I had to go thru this problem several times to finally grasp what to do. We are told that log 50 = 1.699. Just hold that for later. Focus on "log to the base 100 of 50" or \[\log_{100}50 \] and label it with "x=". What do you have at this point?

OpenStudy (katecc379):

sigh i am so confused

OpenStudy (mathmale):

Type out the goal of this problem. Sorry for the repetition, but I want us both to be very clear about what we're looking for here. The goal of this problem is to evaluate .... what? type it out.

OpenStudy (katecc379):

the value of og to the base 100 of 50 when x=1.699

OpenStudy (mathmale):

OK. Let's just say our goal is to evaluate \[\log_{100}50. \]

OpenStudy (mathmale):

I'd like for you to name that (turn it into an equation) by prefacing it with "x="

OpenStudy (katecc379):

log10050=x

OpenStudy (mathmale):

\[or~x=\log_{100 } 50\]

OpenStudy (katecc379):

yes thats what i meant

OpenStudy (mathmale):

Now we want to eliminate that base '100' Write a new equation: 100 = 100 (pretty obvious, no?)

OpenStudy (katecc379):

yes

OpenStudy (mathmale):

Now, for the left 100, use \[\log_{100}50 \] as the exponent.

OpenStudy (mathmale):

\[100^{\log_{100}50 }.\]

OpenStudy (katecc379):

okay

OpenStudy (mathmale):

Can you agree with that?

OpenStudy (mathmale):

Evaluate that. Value=?

OpenStudy (mathmale):

Note: the expo. and log. functions are inverses of one another, so one cancels out (or undoes) the other.

OpenStudy (katecc379):

50

OpenStudy (mathmale):

Excellent. You began with 100 = 100 and raised the first 100 to a certain power, resulting in an overall value of 50. Now, raise the right-hand '100" to the power x. Recall that \[\log_{100}50=x \] as we agreed earlier.

OpenStudy (katecc379):

okay so 100^1.699???

OpenStudy (mathmale):

No, but rather 100^x

OpenStudy (mathmale):

You should have 50=100^x. Do you?

OpenStudy (katecc379):

sure lol

OpenStudy (mathmale):

Kool.

OpenStudy (katecc379):

so now what

OpenStudy (mathmale):

now take the common log of 50=100^x (both sides)

OpenStudy (katecc379):

ok

OpenStudy (mathmale):

what do you get, taking the common log of both sides of 50=100^x? Which rule or rules of logs are you going apply here?

OpenStudy (katecc379):

gosh i really have no clue this is making it so confusing

OpenStudy (mathmale):

sorry. At least this is almost our very last step. Have 50=100^x. Must take log of both sides: log 50 = x log 100. OK with that?

OpenStudy (katecc379):

yea

OpenStudy (katecc379):

so log50/log100

OpenStudy (mathmale):

If log 50=xlog 100, solve for x. Hint: rewrite 100 as 10^2 first.

OpenStudy (mathmale):

log 50=xlog ( ? )

OpenStudy (katecc379):

what???

OpenStudy (mathmale):

Sorry. We're on track; it's just a bit hard to follow. 50=100^x. 50=(10^2)^x. Agreed? Isn't 100=10^2?

OpenStudy (katecc379):

yea

OpenStudy (mathmale):

Then log 50=log (10^2). Can you simplify the right side?

OpenStudy (katecc379):

2

OpenStudy (mathmale):

yes. log 10^2 = 2 log 10 = 2(1) = 2. very good. Then log 50=2x, right?

OpenStudy (katecc379):

yes

OpenStudy (mathmale):

solve that for x, please

OpenStudy (katecc379):

-2log5

OpenStudy (mathmale):

??

OpenStudy (katecc379):

log2=-2log5

OpenStudy (mathmale):

\[\log_{10} 50=2x\]

OpenStudy (mathmale):

Divde both sides by 2, please

OpenStudy (katecc379):

log5/2

OpenStudy (mathmale):

?? unsure of how you got that. If log 50=2x, then \[\frac{ \log_{10}50 }{ 2 }=x=?\]

OpenStudy (mathmale):

recall that we already know the value of log 50. Substitute that value for log 50 in the above equation.

OpenStudy (katecc379):

god i dont even know anymore

OpenStudy (mathmale):

Review the original question we've been working on. The value of log 50 is given there.

OpenStudy (mathmale):

log 50=?

OpenStudy (katecc379):

1.699

OpenStudy (mathmale):

right. What is x=1.699/2?

OpenStudy (katecc379):

.8495

OpenStudy (mathmale):

that's right. That's your answer.

OpenStudy (katecc379):

woww finallyyyyy

OpenStudy (mathmale):

Yes. As I said, I had to go thru this a couple of times too recall what to do.

OpenStudy (mathmale):

You begin with\[\log_{100}50 \] as your unknown and name it 'x'

OpenStudy (mathmale):

So \[\log_{100}50=x \]

OpenStudy (mathmale):

Use the 2 sides of this equation as exponents for the equation 100 = 100. Follow me? I'm just summarizing what we've already done.

OpenStudy (mathmale):

\[100^{\log_{100}50 }=100^{x}\]

OpenStudy (mathmale):

OK?

OpenStudy (mathmale):

Good idea to copy down this summary for later ref.

OpenStudy (mathmale):

OK?

OpenStudy (mathmale):

I was going to review this problem very quickly to help you consolidate what you've learned. Guess something else has caught your attention. Enjoyed working with you.

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