Question

A straight line $$L$$ with negative slope passes through the point $$\left( {8,\,2} \right)$$  and cuts the positive coordinate axes at points $$P$$ and $$Q.$$ As $$L$$ varies the absolute minimum value of $$OP + OQ$$   is ($$O$$ is origin)

A. 28
B. 15
C. 18  
D. 10
Answer :   18
Solution :
Let the equation of the line $$L$$ be $$y - 2 = m\left( {x - 8} \right),\,m < 0$$
Coordinates of $$P$$ and $$Q$$ are $$P\left( {8 - \frac{2}{m},\,0} \right)$$   and $$Q\left( {0,\,2 - 8m} \right)$$
$$\eqalign{ & {\text{So, }}OP + OQ = 8 - \frac{2}{m} + 2 - 8m = 10 + \frac{2}{{ - m}} + 8\left( { - m} \right) \cr & \geqslant 10 + 2\sqrt {\frac{2}{{ - m}} + 8\left( { - m} \right)} \geqslant 18 \cr} $$
absolute min. value of $$OP + OQ = 18.$$

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

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Straight Lines


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