+0  
 
0
1387
1
avatar

Solve for x:

log2x+1=log4x 

 

I know the answer is 1/4 but I don't know how to get there. Help please.

 Sep 7, 2014

Best Answer 

 #1
avatar+129839 
+5

If we have log(2x+1)=log(4x). we can just set 2x + 1  =  4x and solve

So we have

2x + 1 = 4x

1 = 2x

 x = 1/2

------------------------------------------------------------------------------------------------

If we have log(2x)+1=log(4x)  .....we have (writing "1" as "log 10" )

log(2x)+ log 10 = log4x    and by a property of logs, we can write

log(2x*10) = log(4x)

log (20x) = log(4x)

And setting 20x = 4x   →    x = 0     ......but this answer isn't possible because we would be taking the log of 0 and that's undefined......so..... log(2x)+1=log(4x) has no solution....

 

The graph of the second situation can be seen here.....https://www.desmos.com/calculator/cdqfqzhvpa

Note that the graphs never intersect......thus, there are no solution points......

 

 Sep 7, 2014
 #1
avatar+129839 
+5
Best Answer

If we have log(2x+1)=log(4x). we can just set 2x + 1  =  4x and solve

So we have

2x + 1 = 4x

1 = 2x

 x = 1/2

------------------------------------------------------------------------------------------------

If we have log(2x)+1=log(4x)  .....we have (writing "1" as "log 10" )

log(2x)+ log 10 = log4x    and by a property of logs, we can write

log(2x*10) = log(4x)

log (20x) = log(4x)

And setting 20x = 4x   →    x = 0     ......but this answer isn't possible because we would be taking the log of 0 and that's undefined......so..... log(2x)+1=log(4x) has no solution....

 

The graph of the second situation can be seen here.....https://www.desmos.com/calculator/cdqfqzhvpa

Note that the graphs never intersect......thus, there are no solution points......

 

CPhill Sep 7, 2014

0 Online Users