derive the equation of the parabola for which y=1 is the directrix and F(3,-2) is the focus
Question
Derive the equation of the parabola for which
- Directrix: y = 1
- Focus: F(3, -2)
Solution
Sure, let's derive the equation of the parabola step by step.
The general equation of a parabola is given by (x-h)² = 4a(y-k), where (h,k) is the vertex of the parabola and 'a' is the distance from the vertex to the focus or from the vertex to the directrix.
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The directrix of the parabola is y = 1 and the focus is F(3,-2). The vertex of the parabola is always halfway between the focus and the directrix. So, the y-coordinate of the vertex is the average of the y-coordinate of the focus and the directrix, which is (-2+1)/2 = -0.5. The x-coordinate of the vertex is the same as the x-coordinate of the focus, which is 3. So, the vertex (h,k) of the parabola is (3,-0.5).
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The value of 'a' is the distance from the vertex to the focus or from the vertex to the directrix. So, a = |-0.5 - (-2)| = 1.5.
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Substituting h = 3, k = -0.5, and a = 1.5 into the general equation of a parabola, we get (x-3)² = 4*1.5(y - (-0.5)).
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Simplifying this equation, we get (x-3)² = 6(y + 0.5).
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Further simplifying, we get (x-3)² = 6y + 3.
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Finally, subtracting 3 from both sides, we get (x-3)² - 3 = 6y.
So, the equation of the parabola for which y=1 is the directrix and F(3,-2) is the focus is (x-3)² - 3 = 6y.
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