document.write( "Question 685572: log5(x+7)+log5(x-7)=2 \n" ); document.write( "

Algebra.Com's Answer #424500 by josmiceli(19441) $\"\"$ $\"About$

You can put this solution on YOUR website!
The trick is to use $\"+log%285%2C25%29+=+2+\"$ , then
\n" ); document.write( " $\"+log%285%2C%28x%2B7%29%29+%2B+log%285%2C%28x-7%29%29+=+2+\"$
\n" ); document.write( " $\"+log%285%2C%28x%2B7%29%29+%2B+log%285%2C%28x-7%29%29+=+log%285%2C25%29+\"$
\n" ); document.write( " $\"+log%28+5%2C+%28x%2B7%29%2A%28x-7%29+%29+=+log%28+5%2C25+%29+\"$
\n" ); document.write( " $\"+log%28+5%2C+x%5E2+-+49+%29+=+log%28+5%2C25+%29+\"$
\n" ); document.write( " $\"+x%5E2+-+49+=+25+\"$
\n" ); document.write( " $\"+x%5E2+=+74+\"$
\n" ); document.write( " $\"+x+=+8.6023+\"$
\n" ); document.write( "( There is a negative solution, too, but I can't use it
\n" ); document.write( "since that would give me log( 5, negative number ) ,
\n" ); document.write( "and there is no log to a positive base that can give
\n" ); document.write( "me a negative number.
\n" ); document.write( "--------------
\n" ); document.write( "check answer:
\n" ); document.write( " $\"+log%28+5%2C%288.6023%2B7%29%29+%2B+log%28+5%2C%288.6023-7%29%29+=+2+\"$
\n" ); document.write( " $\"+log%28+5%2C%28+15.6023+%29%29+%2B+log%28+5%2C%28+1.6023+%29%29+=+2+\"$
\n" ); document.write( " $\"+log%28+5%2C+24.9996+%29+=+2+\"$
\n" ); document.write( "I think the error is due to rounding off
\n" ); document.write( " \n" ); document.write( "

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