Tag: introduction to three dimensional geometry

Questions Related to introduction to three dimensional geometry

$P$ and $Q$ are points on the line joining $A(-2,5)$ and $B(3,1)$ such that $AP=PQ=QB$. Then, the distance of the midpoint of $PQ$ from the origin is

  1. $3$

  2. $\frac {\sqrt 37}{4}$

  3. $4$

  4. $3.5$


Correct Option: B

A line passes through two point $A (2, -3, -1)$ and $B (8, -1, 2)$. The coordinates of a point on this line at a distance of $14$ units from $A$ are

  1. $(14, 1, 5)$

  2. $(-10, -7, 7)$

  3. $(86, 25, 41)$

  4. None of these


Correct Option: A
Explanation:

Given points are $A(2,-3,-1)$ and $B(8,-1,2)$
Therefore direction  ratio of $AB$ are $l = \dfrac{6}{7}, m=\dfrac{2}{7},n= \dfrac{3}{7}$ or $l=\dfrac{-6}{7},m= \dfrac{-2}{7},n= \dfrac{-3}{7}$
Hence, coordinates of a point $14$ unit from point $A$ is given as,$(2+14l,-3+14m,-1+14n)$
$\Rightarrow (14,1,5)$ or $(-10,-7,-7)$
Hence, option 'A' is correct.

If  $C _1:{x^2+y^2}-20x+64=0$ and $C _2:{x^2+y^2}+30x+144=0$. Then the length of the shortest line segment $PQ$  which touches $C _1$ at $P$ and  to  $C _2$ at $Q$ is

  1. $10$

  2. $15$

  3. $22$

  4. $27$


Correct Option: A
Explanation:

Given $C _1 : x^2+y^2-20x+64=0 \Rightarrow (x-10)^2+y^2=36$
and $C _2 : x^2+y^2+30x+144=0 \Rightarrow (x+15)^2+y^2=81$
So centre and radius of $C _1$ and $C _2$ are $(10,0)$, $(-15,0)$ and $6,9$ respectively.
Then, distance between $C _1$ and $C _2$ is $\sqrt{(15+10)^{2}+(0-0)^{2}}=25$. 

$PQ$ touches $C _{1}$ at $P$ and $C _{2}$ at $Q$.
Then, shortest length of $PQ$ is $=25-(9+6)=25-15=10$

The distance of the point $(4,7)$ from the $x-$ axis is 

  1. $4$

  2. $7$

  3. $11$

  4. $\sqrt{65}$


Correct Option: A

Minimum distance between the curves
$y^{2}=4x$ & $x^{2}+y^{2} -12x+31=0$ is -

  1. $\sqrt {21}$

  2. $\sqrt {26}-\sqrt {5}$

  3. $\sqrt {20}-\sqrt {5}$

  4. $\sqrt {21}-\sqrt {5}$


Correct Option: A

The distance of the point $(2,3)$ form the line $x-2y+5=0$ measured in a direction parallel to the line $x-3y=0$ is

  1. $2\sqrt{10}$

  2. $\sqrt{10}$

  3. $2\sqrt{5}$

  4. $None\ of\ these$


Correct Option: A

The distance of the point $(2,1,-1)$ from the line $\dfrac{x-1}{2}=\dfrac{y+1}{1}=\dfrac{z-3}{-3}$ measured parallel to the plane $x+2y+z=4$ is

  1. $\sqrt{10}$

  2. $\sqrt{20}$

  3. $\sqrt{5}$

  4. $\sqrt{30}$


Correct Option: A

The distance of the point (1,3) from the line 2x-3y+9=0 measured along a line x-y+1=0 is

  1. $\sqrt 2$

  2. $\sqrt 5$

  3. $2\sqrt 2$

  4. 1


Correct Option: A

If $L _1$ is the line of intersection of the plane $2x-2y+3z-2=0, x-y+z+1=0$ and $L _2$ is the line of intersection of the plane   $x+2y-z-3=0, 3x-y+2z-1=0$, then the distance of origin from from the plane containing the lines $L _1$ + $L _2$ is :

  1. $\dfrac{1}{\sqrt{2}}$

  2. $\dfrac{1}{4\sqrt{2}}$

  3. $\dfrac{1}{2\sqrt{2}}$

  4. none of these


Correct Option: A

The equation of plane which is passing through the point $(1,2,3)$ and which is at maximum distance from the point $(-1,0,2)$ is

  1. $2x+2y+z=9$

  2. $2x+z=5$

  3. $3x+y-z=2$

  4. none of these


Correct Option: A