$\"\"$

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The conic has focus at origin.

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The eccentricity of the conic is $\"\"$ .

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The directrix is $\"\"$ .

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Let $\"\"$ be a fixed point and $\"\"$ be a fixed line (directrix) in a plane.

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Let $\"\"$ be a fixed positive number (called the eccentricity). The set of all points $\"\"$ in the plane such that $\"\"$ .

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$\"\"$

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Observe the diagram:

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Substitute $\"\"$ and $\"\"$ .

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$

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$\"\"$ .

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$\"\"$

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$\"\"$ .