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Mathematics 13 Online
OpenStudy (anonymous):

someone please help me fan, medal, testimony

OpenStudy (anonymous):

OpenStudy (phi):

what do you multiply by to get from the number of runs in year 1 to # in year 2 ?

OpenStudy (anonymous):

multiply by 2? @phi

OpenStudy (phi):

yes. when you multiply (like in this problem) to get to the next number, that means think exponents the multiply by 2 should be the hint: 2 2*2 2*2*2 are the first 3 entries. match those with the year 1 2 2 2*2 3 2*2*2 do you see a pattern ?

OpenStudy (anonymous):

not really ): that was kinda confusing. ):

OpenStudy (phi):

for year 4, how many runs do you expect to see (based on the pattern) ?

OpenStudy (phi):

1 2 2 2*2 3 2*2*2 4 ?

OpenStudy (anonymous):

2*2*2*2

OpenStudy (phi):

yes, and can you exponents to write the "short way" ?

OpenStudy (phi):

if you multiply something by itself 4 times 2*2*2*2 then using exponents (because people wanted a short way to write this) \[ 2^4 \]

OpenStudy (phi):

so your table could be written like this \[ 1 \ 2^1 \\ 2\ 2^2 \\ 3\ 2^3 \\ 4\ 2^4 \] or if you use "x" as the year \[ x \ 2^x \]

OpenStudy (phi):

for year "x", the number of runs will be \[ runs= 2^x \]

OpenStudy (anonymous):

I understand now(: but how would I be able to put that in words? to complete the question. the only part im confused about now, is the number I am given (256)

OpenStudy (phi):

to "explain how to create an exponential function" I would say number of runs for year x is 2^x, so the exponential function is r = 2^x where x is the year and r is the number of runs to convert to a "logarithmic function", take the logarithm of both sides log_2(r) = x or if we use log base e ln(r) = x ln(2) \[ \frac{\ln(r)}{\ln(x)} =x \]

OpenStudy (phi):

to solve for the year when r = 256 we can take the log base 2 of 256 \[ x= \log_2(256) \] if you know your powers of 2 you can answer that. but if you need a calculator, you need to change to base 10 or base e \[ x = \frac{\ln(256)}{\ln(2)} \]

OpenStudy (anonymous):

wait, so all I do is plug 256/2 into the calculator? @phi

OpenStudy (phi):

no. unfortunately logs are confusing what you are trying to figure out is how many 2's to multiply to get 256 2*2*2*2*2...*2 how many ? one way is keep multiplying and count how many 2's you need

OpenStudy (anonymous):

its 2 x 2 x 2 x 2 x 2 x 2 x 2 x 2 = 256 so because I know its multipled by 2, 8 times, where do I go from there?

OpenStudy (phi):

count how many 2's you used

OpenStudy (anonymous):

8

OpenStudy (phi):

8, so that is the answer year 8 is when you get 256 runs

OpenStudy (phi):

in other words \[ 256= 2^8 \] and log base 2 of 2^8 means "tell me what the exponent is" the exponent is 8

OpenStudy (phi):

if you need to use a calculator (which does not know base 2) you can use base 10 (for example) type log(256) that gives you the exponent for 10 (which is not 2) then divide that number by log(2) you should get 8

OpenStudy (anonymous):

thank you so much

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