<https://www.physicsforums.com/threads/question-involving-calculations-with-a-parabola.980837/>
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"Summary:  Find the equation of the parabola when the focus and the equation of tangent at the vertex is known.\n\nFind the equation of the parabola when the focus is ##(0,0)## and the equation of tangent at the vertex is ##x - y + 1 = 0##.\n\nGeneral equation : ## ax^2 + by^2 + 2hxy + 2gx + 2fy + c = 0##\nApart from this I have another question. It is given in my textbook that ##h^2 - ab = 0## for the general equation to represent parabola. Why or from where is this derived?"
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