Single Choice

The foot of the perpendicular drawn from the origin, on the line, $$3x + y = \lambda (\lambda \neq 0)$$ is $$P$$. If the line meets x-axis at $$A$$ and y-axis at $$B$$, then the ratio $$BP : PA$$ is

A$$9 : 1$$
Correct Answer
B$$1 : 3$$
C$$1 : 9$$
D$$3 : 1$$

Solution

Let (x,y) be foot of perpendicular drawn to the point $$(x_1,y_1)$$ on the line $$ax+by+c=0$$

Relation :$$\dfrac{x-x_{1}}{a}=\dfrac{y-y_{1}}{b}=\dfrac{-\left ( ax_{1}+by_{1}+cz_{1} \right )}{a^{2}+b^{2}}$$

Here $$(x_1,y_1)$$=(0,0)
given line is: $$3x+y-\lambda=0$$

$$\dfrac{x-0}{3}=\dfrac{y-0}{1}=\dfrac{-\left ( \left ( 3\times 0 \right )+\left ( 1\times 0 \right )-\lambda \right )}{3^{2}+1^{2}}$$

$$x=\dfrac{3\lambda }{10}$$ and $$y=\dfrac{\lambda }{10}$$

Hence foot of perpendicular $$P=\left ( \dfrac{3\lambda }{10},\dfrac{\lambda }{10} \right )$$

Line meets X-axis at $$A=\left ( \dfrac{\lambda }{3},0 \right )$$
and meets Y-axis at $$B=\left ( 0,\lambda \right )$$

$$BP=\sqrt{\left ( \dfrac{3\lambda }{10} \right )^{2}+\left ( \dfrac{\lambda }{10}-\lambda \right )^{2}}$$

$$\Rightarrow BP=\sqrt{\dfrac{9\lambda ^{2}}{100}+\dfrac{81\lambda ^{2}}{100}}$$

$$\therefore BP=\sqrt{\dfrac{90\lambda ^{2}}{100}}$$

$$AP=\sqrt{\left ( \dfrac{\lambda }{3}-\dfrac{3\lambda }{10} \right )^{2}+\left ( 0-\dfrac{\lambda }{10} \right )^{2}}$$

$$\Rightarrow AP=\sqrt{\dfrac{\lambda ^{2}}{900}+\dfrac{\lambda ^{2}}{100}}$$

$$\therefore AP=\sqrt{\dfrac{10\lambda ^{2}}{900}}$$

$$\therefore BP:AP=9:1$$

Hence,correct option is 'A'.


SIMILAR QUESTIONS

Straight Lines and Pair of Straight Lines

Let $$a$$ and $$b$$ be any two numbers satisfying $$\dfrac {1}{a^2}+\dfrac {1}{b^2}=\dfrac {1}{4}$$. Then, the foot of perpendicular from the origin on the variable line, $$\dfrac {x}{a}+\dfrac {y}{b}=1$$, lies on :

Straight Lines and Pair of Straight Lines

The foot of the perpendicular from the point $$(3, 4)$$ on the line $$3x-4y+5=0$$ is:

Straight Lines and Pair of Straight Lines

The ends $$A, B$$ of a straight line segment of constant length $$c$$ slide upon the fixed rectangular axes $$OX$$ & $$OY$$ respectively. If the rectangle $$OAPB$$ be completed then, the locus of the foot of the perpendicular drawn from $$P$$ to $$AB$$ is ?

Straight Lines and Pair of Straight Lines

A straight line passes through a fixed point $$(h,k)$$. Find the locus of feet of the perpendiculars, drawn from the origin to it.

Straight Lines and Pair of Straight Lines

If $$p$$ and $$p'$$ be the lengths of perpendiculars from origin to the lines $$x \sec \theta-y \cos\theta=a$$ and $$x \cos \theta-y \sin \theta=a \cos 2\theta$$ respectively, then prove that $$4p^{ 2 }+p' ^{ 2 }=a^{ a }$$.

Straight Lines and Pair of Straight Lines

Prove that the product of the perpendiculars from the point $$ \left[ \pm \sqrt { \left( { a }^{ 2 }-{ b }^{ 2 } \right) } ,0 \right]$$ to the line $$\dfrac{ x }{ a }\cos \theta+\dfrac{ y }{ b }\sin \theta=1$$ is $$b^{ 2 }$$.

Straight Lines and Pair of Straight Lines

If $$x \cos \alpha + y \sin \alpha = p$$ where, $$p=\dfrac{ \sin^{ 2 }\alpha }{ \cos \alpha }$$ be a straight line, prove that perpendiculars $$p_{ 1 },p_{ 2 }$$ and $$ p_{ 3 }$$ on this line from the points $$(m^{ 2 }, 2m), (mm,m+m)$$ and $$(m^{ 2 },2m)$$ respectively are in geometrical progression.

Straight Lines and Pair of Straight Lines

Find the co-ordinates of the foot of the perpendicular drawn from the point$$(2,3)$$to the line $$y=3x+4$$

Straight Lines and Pair of Straight Lines

Let $$\triangle ABC$$ be a triangle with $$AB = AC$$. If $$D$$ is the midpoint of $$BC$$, $$E$$ is the foot of the perpendicular drawn from $$D$$ to $$AC$$ and $$F$$ the mid-point of $$DE$$. Then $$AF$$ is perpendicular to

Straight Lines and Pair of Straight Lines

The vertices of a triangle OBC are 0(0,0), B (-3, -1), C (- 1,- 3). Find the equation of the line parallel to BC and intersecting the sides OB and OC and whose perpendicular distance from the point (0 , 0) is 1/2.

Contact Details