Question

In triangle $$ABC$$  given $$9{a^2} + 9{b^2} - 17{c^2} = 0.$$     If $$\frac{{\cot A + \cot B}}{{\cot C}} = \frac{m}{n},$$     then the value of $$\left( {m + n} \right)$$   equals

A. 13  
B. 5
C. 7
D. 9
Answer :   13
Solution :
$$\eqalign{ & \frac{{\cot A + \cot B}}{{\cot C}} = \frac{{\sin \left( {A + B} \right)}}{{\sin A\sin B}} \cdot \frac{{\sin C}}{{\sin C}} \cr & = \frac{{{{\sin }^2}C}}{{\sin A\sin B\cos C}} = \frac{{{c^2}}}{{ab}} \cdot \frac{{2ab}}{{{a^2} + {b^2} - {c^2}}} \cr & = \frac{{2{c^2}}}{{{a^2} + {b^2} - {c^2}}} = \frac{{2{c^2}}}{{\frac{{17{c^2}}}{9} - {c^2}}} = \frac{9}{4} = \frac{m}{n} \cr & \Rightarrow \left( {m + n} \right) = 9 + 4 = 13 \cr} $$

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. $$\sqrt {\frac{2}{3}} $$

Practice More Releted MCQ Question on
Properties and Solutons of Triangle


Practice More MCQ Question on Maths Section