Question

In a $$\Delta \,ABC,$$   if $$\frac{{\cos A}}{a} = \frac{{\cos B}}{b} = \frac{{\cos C}}{c},$$      and the side $$a = 2,$$  then are $$a$$ of the triangle is

A. $$1$$
B. $$2$$
C. $$\frac{{\sqrt 3 }}{2}$$
D. $$\sqrt 3 $$  
Answer :   $$\sqrt 3 $$
Solution :
$$\eqalign{ & \frac{{\cos A}}{a} = \frac{{\cos B}}{b} = \frac{{\cos C}}{c} \cr & \Rightarrow \frac{{\cos A}}{{2R\sin A}} = \frac{{\cos B}}{{2R\sin B}} = \frac{{\cos C}}{{2R\sin C}} \cr & \Rightarrow \cot A = \cot B = \cot C \cr & \Rightarrow A = B = C = {60^ \circ } \cr & \Rightarrow \Delta \,ABC{\text{ is equilateral}} \cr & {\text{Hence}},\,\,\Delta = \frac{{\sqrt 3 }}{4}{a^2} = \sqrt 3 . \cr} $$

Releted MCQ Question on
Trigonometry >> Properties and Solutons of Triangle

Releted Question 1

If the bisector of the angle $$P$$ of a triangle $$PQR$$  meets $$QR$$  in $$S,$$ then

A. $$QS = SR$$
B. $$QS : SR = PR : PQ$$
C. $$QS : SR = PQ : PR$$
D. None of these
Releted Question 2

From the top of a light-house 60 metres high with its base at the sea-level, the angle of depression of a boat is 15°. The distance of the boat from the foot of the light house is

A. $$\left( {\frac{{\sqrt 3 - 1}}{{\sqrt 3 + 1}}} \right)60\,{\text{metres}}$$
B. $$\left( {\frac{{\sqrt 3 + 1}}{{\sqrt 3 - 1}}} \right)60\,{\text{metres}}$$
C. $${\left( {\frac{{\sqrt 3 + 1}}{{\sqrt 3 - 1}}} \right)^2}{\text{metres}}$$
D. none of these
Releted Question 3

In a triangle $$ABC,$$  angle $$A$$ is greater than angle $$B.$$ If the measures of angles $$A$$ and $$B$$ satisfy the equation $$3\sin x - 4{\sin ^3}x - k = 0, 0 < k < 1,$$       then the measure of angle $$C$$ is

A. $$\frac{\pi }{3}$$
B. $$\frac{\pi }{2}$$
C. $$\frac{2\pi }{3}$$
D. $$\frac{5\pi }{6}$$
Releted Question 4

In a triangle $$ABC,$$  $$\angle B = \frac{\pi }{3}{\text{ and }}\angle C = \frac{\pi }{4}.$$     Let $$D$$ divide $$BC$$  internally in the ratio 1 : 3 then $$\frac{{\sin \angle BAD}}{{\sin \angle CAD}}$$   is equal to

A. $$\frac{1}{{\sqrt 6 }}$$
B. $${\frac{1}{3}}$$
C. $$\frac{1}{{\sqrt 3 }}$$
D. $$\sqrt {\frac{2}{3}} $$

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