How do you solve $log x + log (x + 15) = 2$ $logx+log(x+15)=2$ ?

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Answer 1 · 2015-02-04T19:58:13

Supposing the base of the log being $10$ $10$ you can solve it by using:
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So you get (using also the definition of logarithm):

Answer 2 · 2015-02-04T20:07:36

There is an error.

The arguments of the logarithmics have to be positive.

So you had to put two condition:

$x > 0$ $x>0$
$x > - 15$ $x> -15$

they drive us to $x > 0$ $x>0$ .

So, one of the solution you found ( $- 20$ $-20$ ) is not acceptable!

How do you solve logx+log(x+15)=2logx+log(x+15)=2logx+log(x+15)=2?