document.write( "Question 807833: In which direction does the parabola open that has a Vertex at (2, -5) and y-intercept at -17 \n" ); document.write( "
Algebra.Com's Answer #486553 by josmiceli(19441)\"\" \"About 
You can put this solution on YOUR website!
I would say that it opens down because the
\n" ); document.write( "y-intercept is more negative than the
\n" ); document.write( "y-coordinate of the vertex.
\n" ); document.write( "I should be able to prove it
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\n" ); document.write( "I'll say the parabola is:
\n" ); document.write( "\"+f%28x%29+=+a%2Ax%5E2+%2B+b%2Ax+%2B+c+\"
\n" ); document.write( "The vertex is at ( 2,-5)
\n" ); document.write( "\"+%28-b%29%2F%282a%29+=+2+\"
\n" ); document.write( "\"+-b+=+4a+\"
\n" ); document.write( "\"+b+=+-4a+\"
\n" ); document.write( "------------
\n" ); document.write( "I can also say
\n" ); document.write( "\"+-5+=+a%2A2%5E2+%2B+b%2A2+%2B+c+\"
\n" ); document.write( "\"+-5+=+4a+%2B+2b+%2B+c+\"
\n" ); document.write( "\"+-5+=+4a+%2B+2%2A%28-4a%29+%2B+c+\"
\n" ); document.write( "\"+c+=+8a+-+4a+-+5+\"
\n" ); document.write( "\"+c+=+4a+-+5+\"
\n" ); document.write( "-----------------
\n" ); document.write( "And also
\n" ); document.write( "(0,-17)
\n" ); document.write( "\"+-17+=+a%2A0%5E2+%2B+b%2A0+%2B+c+\"
\n" ); document.write( "\"+-17+=+c+\"
\n" ); document.write( "-------------
\n" ); document.write( "\"+c+=+4a+-+5+\"
\n" ); document.write( "\"+-17+=+4a+-+5+\"
\n" ); document.write( "\"+4a+=+-12+\"
\n" ); document.write( "\"+a+=+-3+\"
\n" ); document.write( "-----------
\n" ); document.write( "and
\n" ); document.write( "\"+b+=+-4a+\"
\n" ); document.write( "\"+b+=+-4%2A%28-3%29+\"
\n" ); document.write( "\"+b+=+12+\"
\n" ); document.write( "-----------
\n" ); document.write( "\"+f%28x%29+=+a%2Ax%5E2+%2B+b%2Ax+%2B+c++\"
\n" ); document.write( "\"+f%28x%29+=+-3x%5E2+%2B+12x+-+17+\"
\n" ); document.write( "Does it go through (2,-5) ?
\n" ); document.write( "\"+-5+=+-3%2A2%5E2+%2B+12%2A2+-+17+\"
\n" ); document.write( "\"+-5+=+-12+%2B+24+-+17+\"
\n" ); document.write( "\"+-5+=+12+-+17+\"
\n" ); document.write( "\"+-5+=+-5+\"
\n" ); document.write( "OK
\n" ); document.write( "here's the plot:
\n" ); document.write( "\"+graph%28+400%2C+400%2C+-4%2C+6%2C+-20%2C+5%2C+-3x%5E2+%2B+12x+-+17+%29+\"\r
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