Ellipse 1 Question 5

6. The ellipse E1:x29+y24=1 is inscribed in a rectangle R whose sides are parallel to the coordinate axes. Another ellipse E2 passing through the point (0,4) circumscribes the rectangle R. The eccentricity of the ellipse E2 is

(2012)

(a) 22

(b) 32

(c) 12

(d) 34

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Answer:

Correct Answer: 6. (a)

Solution:

  1. PLAN Equation of an ellipse is x2a2+y2b2=1

Eccentricity

e2=1b2a2

440 Ellipse

Description Situation As ellipse circumscribes the rectangle, then it must pass through all four vertices.

Let the equation of an ellipse E2 be

x2a2+y2b2=1, where a<b and b=4.

Also, it passes through (3,2).

9a2+4b2=1[b=4]9a2+14=1 or a2=12

Eccentricity of E2,e2=1a2b2=11216=14[a<b]

e=12



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