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log2+log(11-x^2)-log(1-x)=0 help

 Apr 18, 2016
 #1
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log2+log(11-x^2)-log(1-x)=0    subtract log(2)  from both sides

 

log(11-x^2)-log(1-x)  = - log 2     and we can use a property of logs to write

 

log [ (11 - x^2) / (1 -x)]  = - log(2)   which means that

 

10-log(2)  = [11 - x^2] / [ 1 - x]

 

1/2  = [11 - x^2] / [ 1 - x ]       multiply both sides by 1 - x

 

(1/2) [ 1 - x ] = 11 - x^2        multiply through by 2

 

1 - x   = 22 - 2x^2       rearrange

 

2x^2 - x - 21  = 0       factor

 

(2x -7) (x + 3)  = 0

 

Setting each factor to 0, the possible answers are x = 7/2  or x = -3

 

We  must reject the first solution because it makes a log negative in the original equation

 

So...the only [real] solution  is   x = -3

 

 

cool cool cool

 Apr 18, 2016

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