Question

If $$x \in \left[ { - \frac{{5\pi }}{2},\frac{{5\pi }}{2}} \right],$$    the greatest positive solution of $$1 + {\sin^4}x = {\cos ^2}3x$$    is

A. $${\pi }$$
B. $${2\pi }$$  
C. $${\frac{{5\pi }}{2}}$$
D. None of these
Answer :   $${2\pi }$$
Solution :
$$\eqalign{ & {\sin^2}3x + {\sin ^4}x = 0\,\,\,{\text{or, }}{\sin ^2}x\left\{ {{{\left( {3 - 4\,{{\sin }^2}x} \right)}^2} + {{\sin }^2}x} \right\} = 0 \cr & \therefore \,\,\sin x = 0 \cr & \Rightarrow \,\,x = n\pi . \cr} $$

Releted MCQ Question on
Trigonometry >> Trignometric Equations

Releted Question 1

The equation $$2\,{\cos ^2}\frac{x}{2}{\sin ^2}x = {x^2} + {x^{ - 2}};0 < x \leqslant \frac{\pi }{2}$$        has

A. no real solution
B. one real solution
C. more than one solution
D. none of these
Releted Question 2

The general solution of the trigonometric equation $$\sin x + \cos x = 1$$    is given by:

A. $$x = 2n\pi ;\,\,n = 0,\,\, \pm 1,\,\, \pm 2\,.....$$
B. $$x = 2n\pi + \frac{\pi }{2};\,\,n = 0,\,\, \pm 1,\,\, \pm 2\,.....$$
C. $$x = n\pi + {\left( { - 1} \right)^n}\,\,\frac{\pi }{4} - \frac{\pi }{4}$$
D. none of these
Releted Question 3

The general solution of $$\sin \,x - 3\,\sin \,2x\, + \sin \,3x\, = \cos x - 3\,\cos \,\,2x + \cos \,3x$$           is

A. $$n\pi + \frac{\pi }{8}$$
B. $$\frac{{n\pi }}{2} + \frac{\pi }{8}$$
C. $${\left( { - 1} \right)^n}\frac{{n\pi }}{2} + \frac{\pi }{8}$$
D. $$2n\pi + {\cos ^{ - 1}}\frac{3}{2}$$
Releted Question 4

Number of solutions of the equation $$\tan x + \sec x = 2\cos x$$     lying in the interval $$\left[ {0,2\pi } \right]$$  is:

A. 0
B. 1
C. 2
D. 3

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