Tuesday, February 22, 2011

`log_5sqrt(x - 4) = 3.2` Solve the equation accurate to three decimal places

To simplify the logarithmic equation: `log_5(sqrt(x-4))=3.2` , recall the logarithm property:  `a^((log_(a)(x))) = x` .


When a logarithm function is raised by the same base, the log cancels out which is what we need to do on the left side of the equation.


As a rule we apply same change on both sides of the equation.


 Raising both sides by base of 5:


`5^(log_5(sqrt(x-4)))= 5^(3.2)`


`sqrt(x-4) = 5^(3.2)`


To cancel out the radical sign, square both sides:


`(sqrt(x-4))^2 = (5^(3.2)) ^2 `  


  `x-4 =5^(6.4)`


`  x= 5^(6.4)+4`


 ` x~~29748.593`  (rounded off to three decimal places)


To check, plug-in `x=29748.593` in `log_5(sqrt(x-4))` :


`log_5(sqrt(29748.593-4))`


`log_5(sqrt(29744.593))`


`log_5(172.4662083)=3.2` which is what we want



So, x=29748.593 is the real solution.


Note:` (x^m)^n= x^((m*n ))`

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