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Question -

Find the equation of the ellipse whose centre is (-2, 3) and whose semi – axis are 3 and 2 when the major axis is (i) parallel to x – axis (ii) parallel to the y – axis.



Answer -

Given:

Centre = (-2, 3)

Semi – axis are 3 and 2

(i) Whenmajor axis is parallel to x-axis

Now let us find the equation to the ellipse.

We know that the equation of the ellipse with centre (p, q)is given by

Since major axis is parallel to x – axis

So, a = 3 and b = 2.

a2 = 9

b2 = 4

So the equation of the ellipse can be given as

4(x2 + 4x + 4) + 9(y2 – 6y +9) = 36

4x2 + 16x + 16 + 9y2 – 54y +81 = 36

4x2 + 9y2 + 16x – 54y + 61 =0

 The equation of the ellipse is 4x2 +9y2 + 16x – 54y + 61 = 0.

(ii) Whenmajor axis is parallel to y-axis

Now let us find the equation to the ellipse.

We know that the equation of the ellipse with centre (p, q)is given by

Since major axis is parallel to y – axis

So, a = 2 and b = 3.

a2 = 4

b2 = 9

So the equation of the ellipse can be given as

9(x2 + 4x + 4) + 4(y2 – 6y +9) = 36

9x2 + 36x + 36 + 4y2 – 24y +36 = 36

9x2 + 4y2 + 36x – 24y + 36 =0

 The equation of the ellipse is 9x2 +4y2 + 36x – 24y + 36 = 0.

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