Calculus/Parabola

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Expert: - 4/8/2010


Question
Find the vertex of the parabola y=-3x(squared)-18x+5.

*I don't know how to sqaure the -3x so I put it in parenthesis. please help, I'm so confused.

Answer
For the parbola y = -3x²- 18x + 5, the square is alt-253.  Squareroots are alt-251.
That is, hold down on the alt key and on the number pad type 253, ² or 251, √.

As for the vertex, since the roots are at (-b±√(b²-4ac))/(2a),
the center is halfway between them.

Thus, the ± can be dropped, so the vertex is at -b/(2a).
Since b is -18 and a is -3, -b/2a is --18/2(-3) = -18/6 = -3.

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