SOLUTION: please help me solve: {{{ log( x ) + log ( (x-15) ) = 2 }}}

Algebra ->  Exponential-and-logarithmic-functions -> SOLUTION: please help me solve: {{{ log( x ) + log ( (x-15) ) = 2 }}}      Log On


   

Question 331639: please help me solve: +log%28+x+%29+%2B+log+%28+%28x-15%29+%29+=+2+
Answer by jrfrunner(365) About Me  (Show Source):
You can put this solution on YOUR website!
+log%28+x+%29+%2B+log+%28+%28x-15%29+%29+=+2+
+log%28+x+%29%2A%28x-15%29+=+2+
log%28%28x%5E2-15x%29%29+=+2+
+10%5E%28log%28x%5E2-15x%29%29+=+10%5E2+
+x%5E2-15x+=+100+
+x%5E2+-+15x+-+100+=0+ factor
(x-20)*(x+5)=0
either X=20 or X=-5
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check X=20, by substituting in original equation
Log 20 + log(20-15) =2
log 20 +log 5=2
log+20%2A5=log+100=log+10%5E2+=2
2log10=2
2=2 verifies X=20 as a solution
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check X=-5
log(-5)+log(-5-15)=2 STOP!!!! log functions are define for values greater than 0,
so X=-5 is not a solution