If any point on an ellipse is (3sin\(\alpha\), 5cos\(\alpha\)), then what is the eccentricity of the ellipse?

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NDA-I (Mathematics) Official Paper (Held On: 13 Apr, 2025)
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  1. 4/3
  2. 4/5
  3. 3/4
  4. 1/2

Answer (Detailed Solution Below)

Option 2 : 4/5
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Detailed Solution

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Calculation:

Given any point on the ellipse is 3sinα, 5cosα. In the standard parametric form of an ellipse,

\(x = a\,\sinα,\quad y = b\,\cosα\)

we identify

\(a = 3,\quad b = 5 \)

Since (b > a), the semi-major axis is (b = 5) and the semi-minor axis is (a = 3). The eccentricity e of an ellipse is

\(e = \sqrt{\,1 - \frac{(\text{semi-minor})^{2}}{(\text{semi-major})^{2}}\,} = \sqrt{\,1 - \frac{a^{2}}{b^{2}}\,} \)

Substitute (a = 3) and (b = 5):

\(e = \sqrt{\,1 - \frac{3^{2}}{5^{2}}\,} = \sqrt{\,1 - \frac{9}{25}\,} = \sqrt{\frac{16}{25}} = \frac{4}{5} \)

Hence, the correct answer is Option 2.

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