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NDA 2010
Exam
NDA
Year
2010
Subject
Mathematics
Chapter
Ellipse

NDA 2010 · Mathematics · Ellipse

What are the equations of the directrices of the ellipse 25 x^2+16...

What are the equations of the directrices of the ellipse 25x2+16y2=40025 x^2+16 y^2=400 ?

Options

  1. A3x±25=03 x \pm 25=0
  2. B3y±25=03 y \pm 25=0
  3. Cx±15=0x \pm 15=0
  4. Dy±25=0y \pm 25=0

Correct answer

D. y±25=0y \pm 25=0

Step-by-step solution

25x2400+16y2400=1 or x216+y225=1∴a2=16,b2=25∴\frac{25 x^2}{400}+\frac{16 y^2}{400}=1\begin{gathered} \quad \text{ or } \frac{x^2}{16}+\frac{y^2}{25}=1 \\ \therefore \quad a^2=16, b^2=25 \end{gathered}\therefore Eqs. of directrices are y±25=0y \pm 25=0
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