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what is x

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by DanaJ » Thu Apr 30, 2009 9:43 am
2^(x-2) is a common factor for 2^x and 2^(x-2), so you get:

2^x - 2^(x-2) = 2^(x-2) * [2^2 - 1] = 2^(x - 2) * (4 - 1) = 2^(x - 2) * 3 = 3 * 2^13

This means that x - 2 = 13, so x = 15.

And yes, I do believe this question has been answered before...
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by dumb.doofus » Thu Apr 30, 2009 9:52 am
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by deepoe » Thu Apr 30, 2009 10:11 am
I don't understand this:


2^(x-2) * [2^2 - 1] = 2^(x - 2) * (4 - 1) = 2^(x - 2) * 3 = 3 * 2^13


You got: 2^x - 2^(x-2) But how you get [2^2 - 1] ?
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Re: what is x

by kanha81 » Thu Apr 30, 2009 10:20 am
deepoe wrote:2^x – 2^x-2 = 3(2^13), what is x?
a. 9
b. 11
c. 13
d. 15
e. 17





Don't know if this question already have been asked, if so I'M SORRY
:oops:
Deepoe,
Please type your questions clearly!!!

A better way to write this out would be:
Notice the highlighted part!!!!
2^x - 2^(x-2) = 3 (2^13)

2^x * (1- (1/2^2) ) = 3 * (2^13)
2^x * (3/4) = 3 * (2^13)
2^x = (2^2) * (2^13)
2^x = 2^15
x = 15

[D]
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Re: what is x

by deepoe » Thu Apr 30, 2009 10:23 am
kanha81 wrote:
deepoe wrote:2^x – 2^x-2 = 3(2^13), what is x?
a. 9
b. 11
c. 13
d. 15
e. 17





Don't know if this question already have been asked, if so I'M SORRY
:oops:
Deepoe,
Please type your questions clearly!!!

A better way to write this out would be:
Notice the highlighted part!!!!
2^x - 2^(x-2) = 3 (2^13)

2^x * (1- (1/2^2) ) = 3 * (2^13)
2^x * (3/4) = 3 * (2^13)
2^x = (2^2) * (2^13)
2^x = 2^15
x = 15

[D]
Sorry ;)

Could you explain these steps:

2^x * (1- (1/2^2) ) = 3 * (2^13)
2^x * (3/4) = 3 * (2^13)

Thanks!
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by deepoe » Fri May 01, 2009 4:22 am
ah already understand it :D


2^(x-2) = 2^x * 2^-2

So you get 2^x - 2^x * 2^-2
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