Question

A line makes the same angle $$\theta ,$$ with each of the $$x$$ and $$z$$ - axis. If the angle $$\beta ,$$ which it makes with $$y$$ - axis, is such that $${\sin ^2}\beta = 3{\sin ^2}\theta ,$$    then $${\cos ^2}\theta $$  equals

A. $$\frac{2}{5}$$
B. $$\frac{1}{5}$$
C. $$\frac{3}{5}$$  
D. $$\frac{2}{3}$$
Answer :   $$\frac{3}{5}$$
Solution :
The direction cosines of the line are $$\cos \theta ,\cos \beta ,\cos \theta $$
$$\eqalign{ & \therefore \,\,{\cos ^2}\theta + {\cos ^2}\beta + {\cos ^2}\theta = 1 \cr & \Rightarrow \,\,2{\cos ^2}\theta = {\sin ^2}\beta = 3{\sin ^2}\theta \,\,\left( {{\text{given}}} \right) \cr & \Rightarrow \,\,2{\cos ^2}\theta = 3 - 3{\cos ^2}\theta \cr & \therefore \,\,{\cos ^2}\theta = \frac{3}{5} \cr} $$

Releted MCQ Question on
Trigonometry >> Trigonometric Ratio and Identities

Releted Question 1

If $$\tan \theta = - \frac{4}{3},$$   then $$\sin \theta $$  is

A. $$ - \frac{4}{5}{\text{ but not }}\frac{4}{5}$$
B. $$ - \frac{4}{5}{\text{ or }}\frac{4}{5}$$
C. $$ \frac{4}{5}{\text{ but not }} - \frac{4}{5}$$
D. None of these
Releted Question 2

If $$\alpha + \beta + \gamma = 2\pi ,$$    then

A. $$\tan \frac{\alpha }{2} + \tan \frac{ \beta }{2} + \tan \frac{\gamma }{2} = \tan \frac{\alpha }{2}\tan \frac{\beta }{2}\tan \frac{\gamma }{2}$$
B. $$\tan \frac{\alpha }{2}\tan \frac{\beta }{2} + \tan \frac{\beta }{2}\tan \frac{\gamma }{2} + \tan \frac{\gamma }{2}\tan \frac{\alpha }{2} = 1$$
C. $$\tan \frac{\alpha }{2} + \tan \frac{ \beta }{2} + \tan \frac{\gamma }{2} = - \tan \frac{\alpha }{2}\tan \frac{\beta }{2}\tan \frac{\gamma }{2}$$
D. None of these
Releted Question 3

Given $$A = {\sin ^2}\theta + {\cos ^4}\theta $$    then for all real values of $$\theta $$

A. $$1 \leqslant A \leqslant 2$$
B. $$\frac{3}{4} \leqslant A \leqslant 1$$
C. $$\frac{13}{16} \leqslant A \leqslant 1$$
D. $$\frac{3}{4} \leqslant A \leqslant \frac{{13}}{{16}}$$
Releted Question 4

The value of the expression $$\sqrt 3 \,{\text{cosec}}\,{\text{2}}{{\text{0}}^ \circ } - \sec {20^ \circ }$$     is equal to

A. 2
B. $$\frac{{2\sin {{20}^ \circ }}}{{\sin {{40}^ \circ }}}$$
C. 4
D. $$\frac{{4\sin {{20}^ \circ }}}{{\sin {{40}^ \circ }}}$$

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