document.write( "Question 1239: Solve ln(3x+8)=ln(2x+2)+ln(x-2) for x\r
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document.write( "Please help me \n" );
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Algebra.Com's Answer #371 by khwang(438)![]() ![]() ![]() You can put this solution on YOUR website! Given ln(3x+8)=ln(2x+2)+ln(x-2) \n" ); document.write( " Since the right hand side ln(2x+2)+ln(x-2) = ln(2x+2)(x-2) = ln(2x^2 -2x -4), \n" ); document.write( " So,ln(3x+8) = ln(2x^2 -2x -4) and we have\r \n" ); document.write( "\n" ); document.write( " 3x+8 = 2x^2 -2x -4, or 2x^2 -5x -12 = 0. \n" ); document.write( " Factor: (2x + 3)(x - 4) = 0. \n" ); document.write( " So, x = -3/2 or 4 \r \n" ); document.write( "\n" ); document.write( " But by the definition of ln (log), 3x +8 , 2(x+1) and x-2 must be positive. \n" ); document.write( " Hence, x > -8/3, x > -1 and x > 2. Therefore, x must be greater than 2 and \n" ); document.write( " the solution -3/2 is invalid. The only solution is x =4.\r \n" ); document.write( "\n" ); document.write( " Check,when x = 4, ln(3x+8)=ln(2x+2)+ln(x-2) becomes \n" ); document.write( " ln 20 = ln 10 + ln 2 = ln 10*2 ,so 4 is a correct solution of the \n" ); document.write( " given equation. \n" ); document.write( " \n" ); document.write( " \n" ); document.write( " |