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help...

This topic has 2 member replies
goncalo08 Junior | Next Rank: 30 Posts Default Avatar
Joined
18 Oct 2006
Posted:
11 messages

help...

Post Sat Nov 18, 2006 8:28 pm
3^x - 3^x-1 =162, then x(x-1)=

a 12
b 16
c 20
d 30
e 81

i know this is easy but i couldn't get it

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thankont Senior | Next Rank: 100 Posts
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15 Dec 2006
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Post Tue Dec 19, 2006 8:38 am
You could work it out like this:
3^x-3^x-1=162 => 3^x-1*(3-1) = 162 => 3^x-1=81 =>3^x-1=3^4
so x-1=4 and x=5 and x(x-1)=20

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gamemaster Senior | Next Rank: 100 Posts Default Avatar
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03 Sep 2006
Posted:
34 messages
Post Sun Nov 19, 2006 7:20 am
Try this:

3^x-1 = (3^x)/3

3^x - 3^x-1 = 3^x - (3^x)/3 = (2 * 3^x)/3 = 162

=> x = ...

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