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# If X = a Sec θ Cos ϕ, Y = B Sec θ Sin ϕ and Z = C Tan θ, Then X 2 a 2 + Y 2 B 2 - Mathematics

MCQ

If x = a sec θ cos ϕ, y = b sec θ sin ϕ and z = c tan θ, then$\frac{x^2}{a^2} + \frac{y^2}{b^2}$

#### Options

• $\frac{z^2}{c^2}$

• $1 - \frac{z^2}{c^2}$

• $\frac{z^2}{c^2} - 1$

• $1 + \frac{z^2}{c^2}$

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#### Solution

Given:

x= a secθcosΦ

⇒ x/a=secθ cosΦ

y=b sec θ sinΦ

⇒ y/b=secθ sinΦ

z=c tan θ

z/c= tan θ

Now,

(x/a)^2+(y/b)^2-(z/c)^2=(secθ cosΦ)^2+(secθ sin Φ)^2-(tanθ )^2

⇒ x^2/a^2+y^2/b^2-z^2/c^2= sec^2θcos^2 Φ+sec^2θsin^2Φ-tan^2θ

⇒ x^2/a^2+y^2/b^2-z^2/c^2=(sec^2θ cos^2Φ+sec^2θ sin^2 sin^2Φ)-tan^2Φ

⇒ x^2/a^2+y^2/b^2-z^2/c^2=sec^2θ(cos^2Φ+sin^2Φ)-tan^2θ

⇒ x^2/a^2+y^2/b^2-z^2/c^2= sec^2θ(1)-tan^2θ

⇒ x^2/a^2+y^2/b^2-z^2/c^2=sec^2θ-tan^2θ

⇒ x^2/a^2+y^2/b^2-z^2/c^2=1

⇒x^2/a^2+y^2/b^2=1+z^2/c^2

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#### APPEARS IN

RD Sharma Class 10 Maths
Chapter 11 Trigonometric Identities
Q 23 | Page 58
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