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March 7th, 2017, 09:27 AM  #1 
Newbie Joined: Mar 2017 From: Paris Posts: 3 Thanks: 0  Sum equation problem
Hi everyone. I have an equation to solve  don't know how to proceed. $\displaystyle \sum_{i=0}^n(1.1*x)^n=y$ x and y are known values. I need to figure out the value of n. Any tips out there? Thanks 
March 7th, 2017, 09:48 AM  #2  
Senior Member Joined: Sep 2015 From: USA Posts: 1,753 Thanks: 896  Quote:
solving this should be pretty straightforward now.  
March 7th, 2017, 11:11 AM  #3 
Newbie Joined: Mar 2017 From: Paris Posts: 3 Thanks: 0 
Thanks Romsek ! I can now extract n with a logx. Easy. 
March 8th, 2017, 02:26 PM  #4 
Newbie Joined: Mar 2017 From: Paris Posts: 3 Thanks: 0 
Conversely, what about if I am interesting in figure out what is the value of x, knowing all the other variables? This is equivalent to the following: let's say I have : $\displaystyle x^0+x^1+x²+x³=17$ How can I calculate x? If I use the same above formula, I have an equation with x^(n+1)+ax+c. Thanks! 

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