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Question -

Find the equation of the ellipse whose focus is (1, -2), the directrix 3x – 2y + 5 = 0 and eccentricity equal to 1/2.



Answer -

Given:

Focus = (1, -2)

Directrix = 3x – 2y + 5 = 0

Eccentricity = ½

Let P(x, y) be any point on the ellipse.

We know that distance between the points (x1, y1)and (x2, y2) is given as

We also know that the perpendicular distance from the point(x1, y1) to the line ax + by + c = 0 is given as

So,

SP = ePM

SP2 = e2PM2

Upon cross multiplying, we get

52x2 + 52y2 – 104x + 208y +260 = 9x2 + 4y2 – 12xy – 20y + 30x + 25

43x2 + 48y2 + 12xy – 134x +228y + 235 = 0

 The equation of the ellipse is 43x2 +48y2 + 12xy – 134x + 228y + 235 = 0

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