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how to find the value of x for which this statement is true. 4^2x+1=8

 Apr 30, 2015

Best Answer 

 #4
avatar+118609 
+5

You can show this using the calc on the forum.  That way we can see straight away if it is correct :)

 

$${{\mathtt{4}}}^{\left({\mathtt{2}}{\mathtt{\,\times\,}}{\mathtt{x}}\right)}{\mathtt{\,\small\textbf+\,}}{\mathtt{1}} = {\mathtt{8}} \Rightarrow \left\{ \begin{array}{l}{\mathtt{x}} = {\frac{{ln}{\left({\mathtt{\,-\,}}{\sqrt{{\mathtt{7}}}}\right)}}{{ln}{\left({\mathtt{4}}\right)}}}\\
{\mathtt{x}} = {\frac{{ln}{\left({\mathtt{7}}\right)}}{\left({\mathtt{2}}{\mathtt{\,\times\,}}{ln}{\left({\mathtt{4}}\right)}\right)}}\\
\end{array} \right\}$$

 

$${\frac{{ln}{\left({\mathtt{7}}\right)}}{\left({\mathtt{2}}{\mathtt{\,\times\,}}{ln}{\left({\mathtt{4}}\right)}\right)}} = {\mathtt{0.701\: \!838\: \!730\: \!514\: \!401}}$$

 Apr 30, 2015
 #1
avatar+870 
+5

42x+1=8

42x=7

2x=log4(7)

x=$$\frac{\log_4(7)}{2}$$

 Apr 30, 2015
 #2
avatar+118609 
+5

Thanks EinsteinJr

 

The web2 calc will calculate log base 4 but most will not.

This is a more usual approach

42x=7

log42x=log7

2x*log4=log7

2x=log7/log4

x=log7/(2*log4)

the log can be any base so long as they are both the same base .

 Apr 30, 2015
 #3
avatar+870 
+5

So x≈0.701838730514401 (this isn't the exact value, the number being irrationnal)

 Apr 30, 2015
 #4
avatar+118609 
+5
Best Answer

You can show this using the calc on the forum.  That way we can see straight away if it is correct :)

 

$${{\mathtt{4}}}^{\left({\mathtt{2}}{\mathtt{\,\times\,}}{\mathtt{x}}\right)}{\mathtt{\,\small\textbf+\,}}{\mathtt{1}} = {\mathtt{8}} \Rightarrow \left\{ \begin{array}{l}{\mathtt{x}} = {\frac{{ln}{\left({\mathtt{\,-\,}}{\sqrt{{\mathtt{7}}}}\right)}}{{ln}{\left({\mathtt{4}}\right)}}}\\
{\mathtt{x}} = {\frac{{ln}{\left({\mathtt{7}}\right)}}{\left({\mathtt{2}}{\mathtt{\,\times\,}}{ln}{\left({\mathtt{4}}\right)}\right)}}\\
\end{array} \right\}$$

 

$${\frac{{ln}{\left({\mathtt{7}}\right)}}{\left({\mathtt{2}}{\mathtt{\,\times\,}}{ln}{\left({\mathtt{4}}\right)}\right)}} = {\mathtt{0.701\: \!838\: \!730\: \!514\: \!401}}$$

Melody Apr 30, 2015

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