document.write( "Question 1206103: Find an equation in the form y=ax^2+bx+c for the parabola passing through the points (-1,0),(2,-54),(5,-252) \n" ); document.write( "
Algebra.Com's Answer #843332 by greenestamps(13198)\"\" \"About 
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\n" ); document.write( "Plug each (x,y) pair into the general form of the equation to get three equations in a, b, and c; then solve that system of equations.

\n" ); document.write( "(-1,0): \"a-b%2Bc=0\" [1]

\n" ); document.write( "(2,-54): \"4a%2B2b%2Bc=-54\" [2]

\n" ); document.write( "(5,-252): \"25a%2B5b%2Bc=-252\" [3]

\n" ); document.write( "Eliminate c between [1] and [2], and between [2] and [3], to get two equations in a and b.

\n" ); document.write( "[2]-[1]: \"3a%2B3b=-54\" [4]

\n" ); document.write( "[3]-[2]: \"21a%2B3b=-198\" [5]

\n" ); document.write( "Eliminate b between [4] and [5] and solve for a.

\n" ); document.write( "[5]-[4]: \"18a=-144\"

\n" ); document.write( "\"a=-144%2F18=-8\"

\n" ); document.write( "Substitute a=-8 in [4] and solve for b:
\n" ); document.write( "\"-24%2B3b=-54\"
\n" ); document.write( "\"3b=-30\"
\n" ); document.write( "\"b=-10\"

\n" ); document.write( "Substitute a=-8 and b=-10 in [1] and solve for c:
\n" ); document.write( "\"-8%2B10%2Bc=0\"
\n" ); document.write( "\"c=-2\"

\n" ); document.write( "ANSWER: \"y=-8x%5E2-10x-2\"

\n" ); document.write( "Simplified....

\n" ); document.write( "\"y=-2%284x%5E2%2B5x%2B1%29\"
\n" ); document.write( "\"y=-2%28x%2B1%29%284x%2B1%29\"

\n" ); document.write( "CHECK:
\n" ); document.write( "\"f%28-1%29=%28-2%29%280%29%28-3%29=0\"
\n" ); document.write( "\"f%282%29=%28-2%29%283%29%289%29=-54\"
\n" ); document.write( "\"f%285%29=%28-2%29%286%29%2821%29=-252\"

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