document.write( "Question 184671: For what value(s)of k will the graph of y=3x^2+(k+2)x+3 touch the x-axis at exactly one point \n" ); document.write( "
Algebra.Com's Answer #138606 by josmiceli(19441)\"\" \"About 
You can put this solution on YOUR website!
\"y+=+3x%5E2+%2B+%28k%2B2%29x+%2B+3\"
\n" ); document.write( "Instead of 2 roots, \"r%5B1%5D\" and \"r%5B2%5D\",
\n" ); document.write( "There will be a double root, \"r\"
\n" ); document.write( "\"%28x+-+r%29%28x+-+r%29+=+0\"
\n" ); document.write( "\"x%5E2+-+2rx+%2B+r%5E2+=+0\"
\n" ); document.write( "-------------------------
\n" ); document.write( "\"3x%5E2+%2B+%28k%2B2%29x+%2B+3+=+0\"
\n" ); document.write( "\"x%5E2+%2B+%28%28k%2B2%29%2F3%29%2Ax+%2B+1+=+0\"
\n" ); document.write( "I can make the substitutions
\n" ); document.write( "\"%28k%2B2%29%2F3+=+-2r\"
\n" ); document.write( "\"r%5E2+=+1\"
\n" ); document.write( "\"r+=+1\"
\n" ); document.write( "and
\n" ); document.write( "\"r+=+-1\"
\n" ); document.write( "-------------------------
\n" ); document.write( "\"%28k%2B2%29%2F3+=+-2%2A1\"
\n" ); document.write( "\"k+%2B+2+=+-6\"
\n" ); document.write( "\"k+=+-8\"
\n" ); document.write( "and
\n" ); document.write( "\"%28k%2B2%29%2F3+=+-2%2A%28-1%29\"
\n" ); document.write( "\"k+%2B+2+=+6\"
\n" ); document.write( "\"k+=+4\"
\n" ); document.write( "The graph touches the x-axis when \"k+=+-8\" or \"k+=+4\"
\n" ); document.write( "for \"k+=+-8\":
\n" ); document.write( "\"y+=+3x%5E2+%2B+%28k%2B2%29x+%2B+3\"
\n" ); document.write( "\"y+=+3x%5E2+%2B+%28-8%2B2%29x+%2B+3\"
\n" ); document.write( "\"y+=+3x%5E2+-+6x+%2B+3\"
\n" ); document.write( "for \"k+=+4\":
\n" ); document.write( "\"y+=+3x%5E2+%2B+%284%2B2%29x+%2B+3\"
\n" ); document.write( "\"y+=+3x%5E2+%2B+6x+%2B+3\"
\n" ); document.write( "I'll plot both:
\n" ); document.write( " \"+graph%28+500%2C+500%2C+-5%2C+5%2C+-2%2C+8%2C+3x%5E2+-+6x+%2B+3%2C3x%5E2+%2B+6x+%2B+3%29+\"
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