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.
Given that we need to find the equation of the ellipse whose centre is (- 2,3) and whose semi - axis are 3 and 2.
(i) If major axis is parallel to the x - axis.
We know that the equation of the ellipse with centre (p,q) is given by .
Since major axis is parallel to x - axis a2>b2.
So, a = 3 and b = 2.
⇒ a2 = 9
⇒ b2 = 4
The equation of the ellipse is
⇒
⇒
⇒ 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) If major axis is parallel to the y - axis.
We know that the equation of the ellipse with centre (p,q) is given by .
Since major axis is parallel to y - axis b2>a2.
So, a = 2 and b = 3.
⇒ a2 = 4
⇒ b2 = 9
The equation of the ellipse is
⇒
⇒
⇒ 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.