Question

Let $$A\left( {\alpha ,\,\frac{1}{\alpha }} \right),\,B\left( {\beta ,\,\frac{1}{\beta }} \right),\,C\left( {\gamma ,\,\frac{1}{\gamma }} \right)$$       be the vertices of a $$\Delta ABC,$$   where $$\alpha ,\,\beta $$  are the roots of the equation $${x^2} - 6{p_1}x + 2 = 0,\,\beta ,\,\gamma $$     are the roots of the equation $${x^2} - 6{p_2}x + 3 = 0$$    and $$\gamma ,\,\alpha $$  are the roots of the equation $${x^2} - 6{p_3}x + 6 = 0,\,{p_1},\,{p_2},\,{p_3}$$       being positive. Then, the coordinates of the centroid of $$\Delta ABC$$   is :

A. $$\left( {1,\,\frac{{11}}{{18}}} \right)$$
B. $$\left( {0,\,\frac{{11}}{8}} \right)$$
C. $$\left( {2,\,\frac{{11}}{{18}}} \right)$$  
D. None of these
Answer :   $$\left( {2,\,\frac{{11}}{{18}}} \right)$$
Solution :
It is given that $$\alpha ,\,\beta $$  are the roots of the equation $${x^2} - 6{p_1}x + 2 = 0$$
$$\therefore \,\alpha + \beta = 6{p_1},\,\alpha \beta = 2......\left( {\text{i}} \right)$$
$$\beta ,\,\gamma $$  are the roots of the equation $${x^2} - 6{p_2}x + 3 = 0$$
$$\therefore \,\beta + \gamma = 6{p_2},\,\beta \gamma = 3......\left( {{\text{ii}}} \right)$$
$$\gamma ,\,\alpha $$  are the roots of the equation $${x^2} - 6{p_3}x + 6 = 0$$
$$\therefore \,\gamma + \alpha = 6{p_3},\,\gamma \alpha = 6......\left( {{\text{iii}}} \right)$$
From Equations $$\left( {\text{i}} \right),\,\left( {{\text{ii}}} \right)$$   and $$\left( {{\text{iii}}} \right)$$  we get
$$\eqalign{ & \Rightarrow \alpha \beta \gamma = 6\,\,\,\,\,\left[ {\therefore \,\alpha ,\,\beta ,\,\gamma > 0} \right] \cr & {\text{Now, }}\alpha \beta = 2{\text{ and }}\alpha \beta \gamma = 6 \cr & \Rightarrow \gamma = 3 \cr & \beta \gamma = 3{\text{ }}\,\,{\text{and}}\,\,{\text{ }}\alpha \beta \gamma = 6 \cr & \alpha = 3,\,\,{\text{and }}\alpha = 6\alpha \beta \gamma = 6 \cr & \Rightarrow \beta = 1 \cr & \therefore \alpha + \beta = 6{p_1} \cr & \Rightarrow 3 = 6{p_1} \cr & \Rightarrow {p_1} = \frac{1}{2} \cr & \beta + \gamma = 6{p_2} \cr & \Rightarrow 4 = 6{p_2} \cr & \Rightarrow {p_2} = \frac{2}{3} \cr & {\text{and }}\,\gamma + \alpha = 6{p_3} \cr & \Rightarrow 5 = 6{p_3} \cr & \Rightarrow {p_3} = \frac{5}{6} \cr} $$
The coordinates of the centroid of triangle are
$$\eqalign{ & \left( {\frac{{\alpha + \beta + \gamma }}{3},\,\frac{1}{3}\left( {\frac{1}{\alpha } + \frac{1}{\beta } + \frac{1}{\gamma }} \right)} \right) \cr & {\text{or }}\left( {\frac{6}{3},\,\frac{1}{3}\left( {\frac{1}{2} + 1 + \frac{1}{3}} \right)} \right) \cr & {\text{or }}\left( {2,\,\frac{{11}}{{18}}} \right) \cr} $$

Releted MCQ Question on
Geometry >> Straight Lines

Releted Question 1

The points $$\left( { - a, - b} \right),\left( {0,\,0} \right),\left( {a,\,b} \right)$$     and $$\left( {{a^2},\,ab} \right)$$  are :

A. Collinear
B. Vertices of a parallelogram
C. Vertices of a rectangle
D. None of these
Releted Question 2

The point (4, 1) undergoes the following three transformations successively.
(i) Reflection about the line $$y =x.$$
(ii) Translation through a distance 2 units along the positive direction of $$x$$-axis.
(iii) Rotation through an angle $$\frac{p}{4}$$ about the origin in the counter clockwise direction.
Then the final position of the point is given by the coordinates.

A. $$\left( {\frac{1}{{\sqrt 2 }},\,\frac{7}{{\sqrt 2 }}} \right)$$
B. $$\left( { - \sqrt 2 ,\,7\sqrt 2 } \right)$$
C. $$\left( { - \frac{1}{{\sqrt 2 }},\,\frac{7}{{\sqrt 2 }}} \right)$$
D. $$\left( {\sqrt 2 ,\,7\sqrt 2 } \right)$$
Releted Question 3

The straight lines $$x + y= 0, \,3x + y-4=0,\,x+ 3y-4=0$$         form a triangle which is-

A. isosceles
B. equilateral
C. right angled
D. none of these
Releted Question 4

If $$P = \left( {1,\,0} \right),\,Q = \left( { - 1,\,0} \right)$$     and $$R = \left( {2,\,0} \right)$$  are three given points, then locus of the point $$S$$ satisfying the relation $$S{Q^2} + S{R^2} = 2S{P^2},$$    is-

A. a straight line parallel to $$x$$-axis
B. a circle passing through the origin
C. a circle with the centre at the origin
D. a straight line parallel to $$y$$-axis

Practice More Releted MCQ Question on
Straight Lines


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