document.write( "Question 287399: My problem is:Identify the completing the squares, the vertex, the y-intercept and the axis of symmetry.\r
\n" ); document.write( "\n" ); document.write( "1. y=x^2+6x-11
\n" ); document.write( "2. y=3x^2-x+4
\n" ); document.write( "3. y=2x^2+7x-3
\n" ); document.write( "4. y=2x^2-8x-12\r
\n" ); document.write( "\n" ); document.write( "I need step by step answers\r
\n" ); document.write( "\n" ); document.write( "my email address is gdkpw@hotmail.com
\n" ); document.write( "Thank you
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Algebra.Com's Answer #208286 by josmiceli(19441)\"\" \"About 
You can put this solution on YOUR website!
The best way to think of it is:
\n" ); document.write( "The axis of symmetry is \"x+=+k\" where \"k\"
\n" ); document.write( "is midway between the roots of the equation.
\n" ); document.write( "Then you find the vertex by plugging in \"x=a\"
\n" ); document.write( "back into the equation to get \"y\" , then \"x%2Cy\"
\n" ); document.write( "is the vertex.
\n" ); document.write( "An easy formula is: if the equation is in the form
\n" ); document.write( "\"y+=+ax%5E2+%2B+bx+%2B+c\", then the axis of symmetry is at
\n" ); document.write( "\"x+=+-b%2F%282a%29\"
\n" ); document.write( "The y-intercept is at \"y+=+c\"
\n" ); document.write( "---------------------------------------
\n" ); document.write( "I'll do your 1st problem:
\n" ); document.write( "\"y+=+x%5E2+%2B+6x+-+11\"
\n" ); document.write( "The y-intercept is at \"y+=+-11\"
\n" ); document.write( "Now find roots:
\n" ); document.write( "\"x%5E2+%2B+6x++-+11+=+0\"
\n" ); document.write( "\"x%5E2+%2B+6x+=+11\"
\n" ); document.write( "\"x%5E2+%2B+6x+%2B+%286%2F2%29%5E2+=+11+%2B+%286%2F2%29%5E2\"
\n" ); document.write( "\"x%5E2+%2B+6x+%2B+9+=+11+%2B+9\"
\n" ); document.write( "\"%28x+%2B+3%29%5E2+=+20\"
\n" ); document.write( "\"x+%2B+3+=+sqrt%2820%29\"
\n" ); document.write( "\"x+=+-3+%2B-sqrt%2820%29\"
\n" ); document.write( "The axis of symmetry is midway between the 2 roots which are:
\n" ); document.write( "root1 =\"+-3+%2B+sqrt%2820%29\"
\n" ); document.write( "root2 = \"-3+-+sqrt%2820%29\"
\n" ); document.write( "\"-3\" is midway between these roots, so
\n" ); document.write( "\"x+=+-3\" is the axis of symmetry
\n" ); document.write( "And the simple formula \"x+=+-b%2F%282a%29\" gives the same answer:
\n" ); document.write( "\"a+=+1\"
\n" ); document.write( "\"b+=+6\"
\n" ); document.write( "\"x+=+-6%2F%282%2A1%29\"
\n" ); document.write( "\"x+=+-3\"
\n" ); document.write( "Now plug this result back into the equation:
\n" ); document.write( "\"y+=+x%5E2+%2B+6x+-+11\"
\n" ); document.write( "\"y+=+%28-3%29%5E2+%2B+6%2A%28-3%29+-+11\"
\n" ); document.write( "\"y+=+9+-+18+-+11\"
\n" ); document.write( "\"y+=+-20\"
\n" ); document.write( "So, the vertex is at (-3,-20)
\n" ); document.write( "I'll plot the equation:
\n" ); document.write( "\"+graph%28+500%2C+500%2C+-10%2C+10%2C+-20%2C+20%2C+x%5E2+%2B+6x+-+11%29+\"
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