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Find the coordinates of the foci of the hyperbola \(\rm\frac{y^{2}}{4}-\frac{x^{2}}{9}=1\)
1. \((0, ± \sqrt{13})\)
2. \((0, ± \sqrt{23})\)
3. \((0, ± \sqrt{3})\)
4. \((0, ± \sqrt{33})\)

1 Answer

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Correct Answer - Option 1 : \((0, ± \sqrt{13})\)

Concept:

Hyperbola:

Equation

\(\rm \frac{x^{2}}{a^{2}}-\frac{y^{2}}{b^{2}}=1\)

\(\rm\frac{y^{2}}{a^{2}}-\frac{x^{2}}{b^{2}}=1\)

Equation of Transverse axis

y = 0

x = 0

Equation of Conjugate axis

x = 0

y = 0

Length of Transverse axis

2a

2a

Length of Conjugate axis

2b

2b

Vertices

(± a, 0)

(0, ± a)

Focus

(± ae, 0)

(0, ± ae)

Directrix

x = ± a/e

y = ± a/e

Centre

(0, 0)

(0, 0)

Eccentricity

\(\rm \sqrt{1+\frac{b^{2}}{a^{2}}}\)

\(\rm \sqrt{1+\frac{b^{2}}{a^{2}}}\)

Length of Latus rectum

\(\rm \frac{2b^{2}}{a}\)

\(\rm \frac{2b^{2}}{a}\)

Focal distance of the point (x, y)

ex ± a

ey ± a

 

Calculation:

Given: \(\rm\frac{y^{2}}{4}-\frac{x^{2}}{9}=1\)

It can be written as,

\(\rm⇒ \frac{y^{2}}{4}-\frac{x^{2}}{9}=\frac{y^{2}}{2^{2}}-\frac{x^{2}}{3^{2}}=1\)

On comparing the above equation with the general equation of the hyperbola, \(\rm\frac{y^{2}}{a^{2}}-\frac{x^{2}}{b^{2}}=1\)

⇒ a = 2 and b = 3

As we know that the eccentricity of the hyperbola is  \(\rm \sqrt{1+\frac{b^{2}}{a^{2}}}\).

\(\rm ⇒ \sqrt{1+\frac{b^{2}}{a^{2}}}=\sqrt{1+\frac{3^{2}}{2^{2}}}=\sqrt{\frac{13}{4}}\)

As we know that the coordinates of the foci of the hyperbola \(\rm\frac{y^{2}}{a^{2}}-\frac{x^{2}}{b^{2}}=1\) is (0, ± ae).

\(\rm ⇒(0, ± ae)=(0, ± 2\sqrt{\frac{13}{4}})=(0, ± \sqrt{13})\)

Hence, the correct option is 1.

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