Question : If $x=a\left ( \sin\theta+\cos\theta \right )$ and $y=b\left ( \sin\theta-\cos\theta \right )$, then the value of $\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}$ is:
Option 1: 4
Option 2: 3
Option 3: 1
Option 4: 2
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Correct Answer: 2
Solution : Given: $x=a\left ( \sin\theta+\cos\theta \right )$ and $y=b\left ( \sin\theta-\cos\theta \right )$. $\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}} = \frac{a^{2}\left ( \sin^{2}\theta+2\sin\theta\cos\theta+\cos^{2}\theta \right )}{a^{2}} + \frac{b^{2}\left ( \sin^{2}\theta-2\sin\theta\cos\theta+\cos^{2}\theta \right )}{b^{2}}$ ⇒ $\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}} = \left ( \sin^{2}\theta+2\sin\theta\cos\theta+\cos^{2}\theta \right ) + \left ( \sin^{2}\theta-2\sin\theta\cos\theta+\cos^{2}\theta \right )$ ⇒ $\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}} = 2\sin^{2}\theta+2\cos^{2}\theta$ ⇒ $\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}} = 2(\sin^{2}\theta+\cos^{2}\theta)$ Since $\sin^{2}\theta+\cos^{2}\theta=1$, ⇒ $\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=2$ Hence, the correct answer is 2.
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Question : What is the value of $\frac{\sin \theta+\cos \theta}{\sin \theta-\cos \theta}+\frac{\sin \theta-\cos \theta}{\sin \theta+\cos \theta}$?
Option 1: $\frac{1}{\left(\sin ^2 \theta-\cos ^2 \theta\right)}$
Option 2: $2\left(\sin ^2 \theta-\cos ^2 \theta\right)$
Option 3: $\frac{2}{\left(\sin ^2 \theta-\cos ^2 \theta\right)}$
Option 4: $\sin ^2 \theta-\cos ^2 \theta$
Question : If $x\cos \theta -y\sin \theta =\sqrt{x^{2}+y^{2}}$ and $\frac{\cos ^2{\theta }}{a^{2}}+\frac{\sin ^{2}\theta}{b^{2}}=\frac{1}{x^{2}+y^{2}},$ then the correct relation is:
Option 1: $\frac{x^{2}}{b^{2}}-\frac{y^{2}}{a^{2}}=1$
Option 2: $\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1$
Option 3: $\frac{x^{2}}{b^{2}}+\frac{y^{2}}{a^{2}}=1$
Option 4: $\frac{x^{2}}{a^{2}}-\frac{y^{2}}{b^{2}}=1$
Question : If $x=\operatorname{cosec \theta}-\sin\theta$ and $y=\sec\theta-\cos\theta$, then the relation between $x$ and $y$ is:
Option 1: $x^{2}+y^{2}+3=1$
Option 2: $x^{2}y^{2}\left ( x^{2}+y^{2}+3 \right )=1$
Option 3: $x^{2}\left ( x^{2}+y^{2}-5 \right )=1$
Option 4: $y^{2}\left ( x^{2}+y^{2}-5 \right )=1$
Question : If $\sin \theta \cos \theta=\frac{1}{\sqrt{3}}$ then the value of $\left(\sin ^4 \theta+\cos ^4 \theta\right)$ is:
Option 1: $1$
Option 2: $\frac{5}{3}$
Option 3: $\frac{2}{3}$
Option 4: $\frac{1}{3}$
Question : If $\sin \theta \cos \theta=\frac{\sqrt{2}}{3}$,then the value of $\left(\sin ^6 \theta+\cos ^6 \theta\right)$ is:
Option 1: $\frac{1}{3}$
Option 2: $\frac{4}{3}$
Option 4: $\frac{5}{3}$
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