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How to find the rate (r) of a exponential regression equation?

6872=14592(1+r/1)11

 May 21, 2014

Best Answer 

 #2
avatar+118677 
+5

In all fairness GoldenLeaf you have answered this question very well.

HOWEVER

The question that the asker intended is not the one that you answered. 

The intended question was 

6872=14592(1+r/1)^11

I know this because the word exponential was used in the question.

$$6872=14592(1+r)^{11}\\\\
\frac{6872}{14592}=(1+r)^{11}\\\\
log\left(\frac{6872}{14592}\right)=log(1+r)^{11}\\\\
log\left(\frac{6872}{14592}\right)=11log(1+r)\\\\
\dfrac{log\left(\frac{6872}{14592}\right)}{11}=log(1+r)\\\\
10^{\frac{log\left(\frac{6872}{14592}\right)}{11}}=10^{log(1+r)}\\\\
10^{\frac{log\left(\frac{6872}{14592}\right)}{11}}=1+r\\\\
10^{\frac{log\left(\frac{6872}{14592}\right)}{11}}-1=r\\\\$$

 

$${{\mathtt{10}}}^{\left({\frac{{log}_{10}\left({\frac{{\mathtt{6\,872}}}{{\mathtt{14\,592}}}}\right)}{{\mathtt{11}}}}\right)}{\mathtt{\,-\,}}{\mathtt{1}} = -{\mathtt{0.066\: \!165\: \!642\: \!977\: \!294\: \!8}}$$

 

$$r\approx -0.066$$

 May 21, 2014
 #1
avatar+1006 
+5

Just plug it in!

 

$${\mathtt{6\,872}} = {\mathtt{14\,592}}{\mathtt{\,\times\,}}\left({\mathtt{1}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{r}}}{{\mathtt{1}}}}\right){\mathtt{\,\times\,}}{\mathtt{11}} \Rightarrow {\mathtt{r}} = {\mathtt{\,-\,}}{\frac{{\mathtt{19\,205}}}{{\mathtt{20\,064}}}} \Rightarrow {\mathtt{r}} = -{\mathtt{0.957\: \!187\: \!001\: \!594\: \!896\: \!3}}$$

 

I'll try to show some work, but gimme a sec.

 

As far as I know, we need to isolate the 'r'.

 

First combine like terms.

 

$${\mathtt{6\,872}} = {\mathtt{160\,512}}{\mathtt{\,\times\,}}\left({\mathtt{1}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{r}}}{{\mathtt{1}}}}\right)$$

 

Divide 6872 by 160512

 

$${\frac{{\mathtt{6\,872}}}{{\mathtt{160\,512}}}} = {\mathtt{0.042\: \!812\: \!998\: \!405\: \!103\: \!7}}$$

$${\mathtt{0.042\: \!812\: \!998\: \!405\: \!103\: \!7}} = {\mathtt{1}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{r}}}{{\mathtt{1}}}}$$

 

The 'r/1' can be just 'r'. All that's needed is to subtract 1 from 0.0428129984051037

 

$${\mathtt{0.042\: \!812\: \!998\: \!405\: \!103\: \!7}}{\mathtt{\,-\,}}{\mathtt{1}} = -{\mathtt{0.957\: \!187\: \!001\: \!594\: \!896\: \!3}}$$

$$-{\mathtt{0.957\: \!187\: \!001\: \!594\: \!896\: \!3}} = {\mathtt{r}}$$

 

And thus, the work =)

 May 21, 2014
 #2
avatar+118677 
+5
Best Answer

In all fairness GoldenLeaf you have answered this question very well.

HOWEVER

The question that the asker intended is not the one that you answered. 

The intended question was 

6872=14592(1+r/1)^11

I know this because the word exponential was used in the question.

$$6872=14592(1+r)^{11}\\\\
\frac{6872}{14592}=(1+r)^{11}\\\\
log\left(\frac{6872}{14592}\right)=log(1+r)^{11}\\\\
log\left(\frac{6872}{14592}\right)=11log(1+r)\\\\
\dfrac{log\left(\frac{6872}{14592}\right)}{11}=log(1+r)\\\\
10^{\frac{log\left(\frac{6872}{14592}\right)}{11}}=10^{log(1+r)}\\\\
10^{\frac{log\left(\frac{6872}{14592}\right)}{11}}=1+r\\\\
10^{\frac{log\left(\frac{6872}{14592}\right)}{11}}-1=r\\\\$$

 

$${{\mathtt{10}}}^{\left({\frac{{log}_{10}\left({\frac{{\mathtt{6\,872}}}{{\mathtt{14\,592}}}}\right)}{{\mathtt{11}}}}\right)}{\mathtt{\,-\,}}{\mathtt{1}} = -{\mathtt{0.066\: \!165\: \!642\: \!977\: \!294\: \!8}}$$

 

$$r\approx -0.066$$

Melody May 21, 2014

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