Question

If $$\tan \frac{\pi }{9},x$$   and $$\tan \frac{5\pi }{18}$$  are in A.P. and $$\tan \frac{\pi }{9},y$$   and $$\tan \frac{7\pi }{18}$$  are also in A.P. then

A. $$2x = y$$  
B. $$x > y$$
C. $$x = y$$
D. None of these
Answer :   $$2x = y$$
Solution :
Here, $$2x = \tan {20^ \circ } + \tan {50^ \circ } = \frac{{\sin {{70}^ \circ }}}{{\cos {{20}^ \circ } \cdot \cos {{50}^ \circ }}} = \sec {50^ \circ } = {\text{cosec}}\,{40^ \circ }$$
and $$2y = \tan {20^ \circ } + \tan {70^ \circ } = \frac{{\sin {{90}^ \circ }}}{{\cos {{20}^ \circ } \cdot \cos {{70}^ \circ }}}$$
$$2y = \frac{1}{{\cos {{20}^ \circ } \cdot \sin {{20}^ \circ }}} = \frac{2}{{\sin {{40}^ \circ }}}.$$

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. $$\frac{{4\sin {{20}^ \circ }}}{{\sin {{40}^ \circ }}}$$

Practice More Releted MCQ Question on
Trigonometric Ratio and Identities


Practice More MCQ Question on Maths Section