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log(x,5)+log(2x+3,5)=1,how do I find x?

 Mar 24, 2016
edited by Guest  Mar 24, 2016
edited by Guest  Mar 24, 2016
edited by Guest  Mar 24, 2016
edited by Guest  Mar 24, 2016

Best Answer 

 #1
avatar+23252 
+5

log5(x) + log5(2x + 3)  =  1

 

Since logs are added when the original problem was multiplied, going backwards we have:

 

log5[ x · (2x + 3) ]  =  1

log5( 2x2 + 3x )  =  1

 

Writing the log in exponential notation:

 

2x2 + 3x  =  51

--->   2x2 + 3x  =  5     --->     2x2 + 3x - 5  =  0     --->     (2x + 5)(x - 1)  =  0

                                                                         --->     Either  2x + 5  =  0     or     x - 1  = 0

                                                                         --->     Either     x  =  - 5/2     or     x  =  1

 

Since  log5(x)  is undefined if x is a negative number, the value  -5/2  must be ignored; thus the answer is  x  =  1

 Mar 24, 2016
 #1
avatar+23252 
+5
Best Answer

log5(x) + log5(2x + 3)  =  1

 

Since logs are added when the original problem was multiplied, going backwards we have:

 

log5[ x · (2x + 3) ]  =  1

log5( 2x2 + 3x )  =  1

 

Writing the log in exponential notation:

 

2x2 + 3x  =  51

--->   2x2 + 3x  =  5     --->     2x2 + 3x - 5  =  0     --->     (2x + 5)(x - 1)  =  0

                                                                         --->     Either  2x + 5  =  0     or     x - 1  = 0

                                                                         --->     Either     x  =  - 5/2     or     x  =  1

 

Since  log5(x)  is undefined if x is a negative number, the value  -5/2  must be ignored; thus the answer is  x  =  1

geno3141 Mar 24, 2016

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