document.write( "Question 607150: solve log x+log(x+21)=2 \n" ); document.write( "
Algebra.Com's Answer #382447 by lawdej(58)\"\" \"About 
You can put this solution on YOUR website!
log x+log(x+21)=2
\n" ); document.write( "first determine domain
\n" ); document.write( "domain=x>0 and x>-21=x>0
\n" ); document.write( "log(x*(x+21))=2
\n" ); document.write( "log(x^2+21x)=2
\n" ); document.write( "x^2+21x=10^2
\n" ); document.write( "x^2+21x=100
\n" ); document.write( "x^2+21x-100=0
\n" ); document.write( "x^2-4x+25x-100=0
\n" ); document.write( "x(x-4)+25(x-4)=0
\n" ); document.write( "(x+25)+(x-4)=0
\n" ); document.write( "(x+25)=0 or(x-4)=0
\n" ); document.write( "x=-25 or x=4
\n" ); document.write( "or
\n" ); document.write( "use quadratic formula
\n" ); document.write( "x^2+21x-100=0
\n" ); document.write( "x=(-21+or-square root of (441+400))/2
\n" ); document.write( "x=(-21+or-square root of (841))/2
\n" ); document.write( "x=(-21+or- 29)/2
\n" ); document.write( "x=(-21+29)/2 or x=(-21-29)/2
\n" ); document.write( "x=8/4 or x=-50/2
\n" ); document.write( "x=4 or x=-25
\n" ); document.write( "but the solution is only x=4 since -25 is not in the domain
\n" ); document.write( "(lawdej@yahoo.com) \n" ); document.write( "
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