Q. 94.3( 3 Votes )

# Find the (i) lengths of major axes, (ii) coordinates of the vertices, (iii) coordinates of the foci, (iv) eccentricity, and (v) length of the latus rectum of each of the following ellipses.

3x^{2} + 2y^{2} = 18

Answer :

Given:

3x^{2} + 2y^{2} = 18

Divide by 18 to both the sides, we get

…(i)

Since, 6 < 9

So, above equation is of the form,

…(ii)

Comparing eq. (i) and (ii), we get

a^{2} = 9 and b^{2} = 6

⇒ a = √9 and b = √6

⇒ a = 3 and b = √6

(i) __To find__: Length of major axes

Clearly, a < b, therefore the major axes of the ellipse is along y axes.

∴Length of major axes = 2a

= 2 × 3

= 6 units

(ii) __To find__: Coordinates of the Vertices

Clearly, a > b

∴ Coordinate of vertices = (0, a) and (0, -a)

= (0, 6) and (0, -6)

(iii) __To find__: Coordinates of the foci

We know that,

Coordinates of foci = (0, ±c) where c^{2} = a^{2} – b^{2}

So, firstly we find the value of c

c^{2} = a^{2} – b^{2}

= 9 – 6

c^{2} = 3

c = √3 …(I)

∴ Coordinates of foci = (0, ±√3)

(iv) __To find__: Eccentricity

We know that,

[from (I)]

(v) __To find__: Length of the Latus Rectum

We know that,

= 4

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