Vertex of a ParabolaDate: 04/16/2002 at 22:05:40 From: Chris Subject: Vertex of a Parabola What is the quickest annd easiest way to find the y-coordinate of the vertex? I know that the x-coordinate is -b/2a. Is the best way to plug that value into the equation y = ax^2+bx+c, or is there a special formula that will get the answer quicker? Date: 04/17/2002 at 07:48:25 From: Doctor Floor Subject: Re: Vertex of a Parabola Hi, Chris, Thanks for your question. Of course we can MAKE the formula by plugging in the x-coordinate: y = a(-b/2a)^2 + b*(-b/2a) + c a*b^2 b^2 = ----- - --- + c 4a^2 2a b^2 b^2 = --- - --- + c 4a 2a b^2 = c - --- 4a See also from the Dr. Math archive: Completing the Square http://www.mathforum.org/library/drmath/view/53102.html Here the vertex is derived by completing the square, and is found from the formula given in step 5. If you have more questions, just write back. Best regards, - Doctor Floor, The Math Forum http://mathforum.org/dr.math/ |
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