Saturday 2 August 2014

`log_5(2x-7)=log_5(3x-9)` Solve the equation. Check for extraneous solutions.

`log_5(2x-7)=log_5(3x-9)`


Using one to one property of logarithms,


`2x-7=3x-9`


`=>2x-3x=-9+7`


`=>-x=-2`


`=>x=2`


Let's plug back the solution in the equation,


`log_5(2*2-7)=log_5(3*2-9)`


`log_5(-3)=log_5(-3)`


However logarithm of negative number is undefined,


So the solution is extraneous.

`log_5(2x-7)=log_5(3x-9)`


Using one to one property of logarithms,


`2x-7=3x-9`


`=>2x-3x=-9+7`


`=>-x=-2`


`=>x=2`


Let's plug back the solution in the equation,


`log_5(2*2-7)=log_5(3*2-9)`


`log_5(-3)=log_5(-3)`


However logarithm of negative number is undefined,


So the solution is extraneous.

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