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Problem
For a real number , let be the parabola given by the equation . Prove that all parabolae pass through the same point.
Solution
Let us find a point that lies on all parabolae for any real .
The equation of is .
Let us try to find and such that for all , .
Rewriting: For this to be independent of , the coefficient of must be zero: So, for : Therefore, the point lies on all parabolae .
Thus, all parabolae pass through the same point .
The equation of is .
Let us try to find and such that for all , .
Rewriting: For this to be independent of , the coefficient of must be zero: So, for : Therefore, the point lies on all parabolae .
Thus, all parabolae pass through the same point .
Techniques
Cartesian coordinatesConstructions and loci