SOLUTION: 216^-2k -------- = 36 Please show steps and solution. 36^-2k-3

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Question 1135939: 216^-2k
-------- = 36 Please show steps and solution.
36^-2k-3

Found 4 solutions by Alan3354, Theo, MathTherapy, greenestamps:
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!
What is the exponent in the DEN?

Answer by Theo(13342) About Me  (Show Source):
You can put this solution on YOUR website!
well, .....

i got k = 2 and it appears to be correct.

here's my worksheet.

$$$
$$$

in step 1 i copied the problem.

in step 2 i multiplied both sides of the equation by 36^(-2k-3)

in step 3 i converted 36^(-2k-3) to 36^(-2k) / 36^3 because they're equivalent.

in step 4 i divided 36 in the numerator into 36^3 in the denominator to get 36^2 in the denominator.

in step 5 i replaced (6 * 36)^(-2k) with 6^(-2k) * 36^(-2k) because they're equivalent.

in step 6 i divided both sides of the equation by 36^(-2k) which then removed 36^(-2k) from the equation because 36^(-2k) / 36^(-2k) = 1.

in step 7 i made 6^(-2k) equal to 1 / 6^(2k) because they're equivalent.

in step 8 i cross multiplied.

in step 9 i took the log of both sides of the equation to get log(36^2)( = log(6^(2k)) which then became 2 * log(36) = 2k * log(6) because log(x^a) = a*log(x).

in step 10 i divided both sides of the equation by log(6).

in step 11 i divided both sides of the equation by 2.

in step 12 i solved for k.

any questions how or why i got what i got, send email to dtheophilis@gmail.com.

in donfirmed by replacing k with 2 in the original equation and evaluated it to get 36 = 36.


Answer by MathTherapy(10552) About Me  (Show Source):
You can put this solution on YOUR website!
216^-2k
-------- = 36 Please show steps and solution.
36^-2k-3
If matrix%281%2C3%2C+216%5E%28-+2k%29%2F36%5E%28-+2k+-+3%29%2C+%22=%22%2C+36%29, then:

matrix%281%2C3%2C+6%5E%28-+6k%29%2F6%5E%28-+4k+-+6%29%2C+%22=%22%2C+6%5E2%29
matrix%281%2C3%2C+6%5E%28-+6k+-+%28-+4k+-+6%29%29%2C+%22=%22%2C+6%5E2%29 ----- Applying matrix%281%2C3%2C+a%5Eb%2Fa%5Ec%2C+%22=%22%2C+a%5E%28b+-+c%29%29
- 6k - (- 4k - 6) = 2 ------- Bases are equal and so are the exponents
- 6k + 4k + 6 = 2
- 2k = 2 - 6
- 2k = - 4

You DON'T NEED LOGS or any complex calculations....just the laws of exponents!
Using logs is just a waste of time and effort, unless you're requested to use logs, of course.

Answer by greenestamps(13200) About Me  (Show Source):
You can put this solution on YOUR website!


216%5E%28-2k%29%2F36%5E%28-2k-3%29+=+36

There are of course many paths to solving this equation....

With the negative exponents in both numerator and denominator, I would first switch them to make the exponents positive:

36%5E%282k%2B3%29%2F216%5E%282k%29+=+36

Then, with bases 36=6^2 and 216=6^3 as the bases for the exponents, change every term in the equation to have base 6:

%286%5E2%29%5E%282k%2B3%29%2F%286%5E3%29%5E%282k%29+=+6%5E2

6%5E%284k%2B6%29%2F6%5E%286k%29+=+6%5E2

6%5E%28-2k%2B6%29+=+6%5E2

The bases are the same, so the exponents are equal:

-2k%2B6+=+2
-2k+=+-4
k+=+2