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.

3x2 + 2y2 = 18

Answer :


Given:


3x2 + 2y2 = 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


a2 = 9 and b2 = 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 c2 = a2 – b2


So, firstly we find the value of c


c2 = a2 – b2


= 9 – 6


c2 = 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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