document.write( "Question 186944: please help! i cant solve this log equation.
\n" ); document.write( "
\n" ); document.write( "2 ln x+ ln(x+7) =3 ln(x+1)
\n" ); document.write( "

Algebra.Com's Answer #140117 by jim_thompson5910(35256)\"\" \"About 
You can put this solution on YOUR website!
\"2%2Aln%28x%29%2Bln%28x%2B7%29=3%2Aln%28x%2B1%29\" Start with the given equation.\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Note: the domain here is \"x%3E0\" (since we CANNOT plug in zero or negative values into \"2%2Aln%28x%29\")\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"ln%28x%5E2%29%2Bln%28x%2B7%29=ln%28%28x%2B1%29%5E3%29\" Rewrite the logs using the identity \"y%2Aln%28x%29=ln%28x%5Ey%29\" (ie move the numbers out front the logs to the exponent position)\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"ln%28x%5E2%28x%2B7%29%29=ln%28%28x%2B1%29%5E3%29\" Combine the logs on the left side using the identity \"ln%28A%29%2Bln%28B%29=ln%28A%2AB%29\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x%5E2%28x%2B7%29=%28x%2B1%29%5E3\" Raise both sides as exponents with the base of 'e' (this effectively cancels out the natural logs)\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x%5E2%28x%2B7%29=%28x%2B1%29%28x%2B1%29%28x%2B1%29\" Rewrite \"%28x%2B1%29%5E3\" as \"%28x%2B1%29%28x%2B1%29%28x%2B1%29\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x%5E2%28x%2B7%29=%28x%2B1%29%28x%5E2%2B2x%2B1%29\" FOIL the last two binomials\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x%5E2%28x%2B7%29=x%28x%5E2%2B2x%2B1%29%2B1%28x%5E2%2B2x%2B1%29\" Expand\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x%5E2%28x%2B7%29=x%5E3%2B2x%5E2%2Bx%2Bx%5E2%2B2x%2B1\" Distribute\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x%5E3%2B7x%5E2=x%5E3%2B3x%5E2%2B3x%2B1\" Combine like terms.\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x%5E3%2B7x%5E2-x%5E3-3x%5E2-3x-1=0\" Get everything to the left side.\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"4x%5E2-3x-1=0\" Combine like terms.\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Notice we have a quadratic equation in the form of \"ax%5E2%2Bbx%2Bc\" where \"a=4\", \"b=-3\", and \"c=-1\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Let's use the quadratic formula to solve for x\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x+=+%28-b+%2B-+sqrt%28+b%5E2-4ac+%29%29%2F%282a%29\" Start with the quadratic formula\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x+=+%28-%28-3%29+%2B-+sqrt%28+%28-3%29%5E2-4%284%29%28-1%29+%29%29%2F%282%284%29%29\" Plug in \"a=4\", \"b=-3\", and \"c=-1\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x+=+%283+%2B-+sqrt%28+%28-3%29%5E2-4%284%29%28-1%29+%29%29%2F%282%284%29%29\" Negate \"-3\" to get \"3\". \r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x+=+%283+%2B-+sqrt%28+9-4%284%29%28-1%29+%29%29%2F%282%284%29%29\" Square \"-3\" to get \"9\". \r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x+=+%283+%2B-+sqrt%28+9--16+%29%29%2F%282%284%29%29\" Multiply \"4%284%29%28-1%29\" to get \"-16\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x+=+%283+%2B-+sqrt%28+9%2B16+%29%29%2F%282%284%29%29\" Rewrite \"sqrt%289--16%29\" as \"sqrt%289%2B16%29\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x+=+%283+%2B-+sqrt%28+25+%29%29%2F%282%284%29%29\" Add \"9\" to \"16\" to get \"25\"\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x+=+%283+%2B-+sqrt%28+25+%29%29%2F%288%29\" Multiply \"2\" and \"4\" to get \"8\". \r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x+=+%283+%2B-+5%29%2F%288%29\" Take the square root of \"25\" to get \"5\". \r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x+=+%283+%2B+5%29%2F%288%29\" or \"x+=+%283+-+5%29%2F%288%29\" Break up the expression. \r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x+=+%288%29%2F%288%29\" or \"x+=++%28-2%29%2F%288%29\" Combine like terms. \r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "\"x+=+1\" or \"x+=+-1%2F4\" Simplify. \r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "So the possible answers are \"x+=+1\" or \"x+=+-1%2F4\" \r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "However, since you CANNOT take the natural of a negative number, this means that \"x+=+-1%2F4\" is NOT a solution. \r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "===========================================================\r
\n" ); document.write( "
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "Answer:\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "So the solution is \"x+=+1\"\r
\n" ); document.write( "
\n" ); document.write( "\n" ); document.write( "
\n" ); document.write( "
\n" );