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Find the differential equation of family of all ellipse whose major axis is twice the minor axis

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Question

Find the differential equation of family of all ellipse whose major axis is twice the minor axis

Sum
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Solution

Let the equation of ellipse be

`x^2/"a"^2 + y^2/"b"^2` = 1     ......(i)

Since the major axis is twice the minor axis,

2a = 2(2b)

∴ a = 2b     ......(ii)

Substituting (ii) in (i), we get

`x^2/(2"b")^2 + y^2/"b"^2` = 1

∴ `x^2/(4"b"^2) + y^2/"b"^2` = 1 

∴ x2 + 4y2 = 4b2

Differentiating w.r.t. x, we get

`2x + 8y  ("d"y)/("d"x)` = 0

∴ `x + 4y ("d"y)/("d"x)` = 0, where is the required differential equation.

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Chapter 2.6: Differential Equations - Attempt the following questions I

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