Wednesday 12 October 2016

`1/3log_5(12x)=2` Solve the equation. Check for extraneous solutions.

To evaluate the given equation `1/3log_5(12x)=2` , we may apply logarithm property: `n* log_b(x) = log_b(x^n)` .


`log_5((12x)^(1/3))=2`


Take the "log" on both sides to be able to apply the logarithm property: `a^(log_a(x))=x` .


`5^(log_5((12x)^(1/3)))=5^(2)`


`(12x)^(1/3)= 25`


Cubed both sides to cancel out the fractional exponent.


`((12x)^(1/3))^3= (25)^3`


`(12x)^(1/3*3)=15625`


`(12x)^(3/3)=15625`


`12x =15625`


Divide both sides by `12` .


`(12x)/12 =(15625)/12`


`x =(15625)/12`


Checking: Plug-in `x=(15625)/12` on `1/3log_5(12x)=2` 


`1/3log_5(12*(15625)/12)=?2`


`1/3log_5(15625)=?2`


`log_5(15625^(1/3))=?2`


`log_5(root(3)(15625))=?2`


`log_5(25)=?2`


`log_5(5^2)=?2`


`2log_5(5)=?2`


`2*1=?2`


`2=2...

To evaluate the given equation `1/3log_5(12x)=2` , we may apply logarithm property: `n* log_b(x) = log_b(x^n)` .


`log_5((12x)^(1/3))=2`


Take the "log" on both sides to be able to apply the logarithm property: `a^(log_a(x))=x` .


`5^(log_5((12x)^(1/3)))=5^(2)`


`(12x)^(1/3)= 25`


Cubed both sides to cancel out the fractional exponent.


`((12x)^(1/3))^3= (25)^3`


`(12x)^(1/3*3)=15625`


`(12x)^(3/3)=15625`


`12x =15625`


Divide both sides by `12` .


`(12x)/12 =(15625)/12`


`x =(15625)/12`


Checking: Plug-in `x=(15625)/12` on `1/3log_5(12x)=2` 


`1/3log_5(12*(15625)/12)=?2`


`1/3log_5(15625)=?2`


`log_5(15625^(1/3))=?2`


`log_5(root(3)(15625))=?2`


`log_5(25)=?2`


`log_5(5^2)=?2`


`2log_5(5)=?2`


`2*1=?2`


`2=2 `  TRUE



There is no extraneous solution. The `x=(15625)/12` is a real solution for the given equation `1/3log_5(12x)=2` .


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