Tag: sets, relations and functions

Questions Related to sets, relations and functions

The equation of a line parallel to $x+2y=1$ and passing through the point of intersection of the lines $x-y=4$ and $3x+y=7$ is ?

  1. $x+2y=5$

  2. $4x+8y-1=0$

  3. $4x+8y+1=0$

  4. none of these


Correct Option: B
Explanation:

Let the equation of line parallel to $x+2y=1$ be $y=mx+c$

intersection point of line $x-y=4$ and $3x+y=7$ is given by solving two equation we get $x=\dfrac { 11 }{ 4 } $ and $y=\dfrac { -5 }{ 4 } $
from equation $x+2y=1\ \Rightarrow y=-\dfrac { 1 }{ 2 } x+\dfrac { 1 }{ 2 } $
we get ${ m } _{ 1 }=-\dfrac { 1 }{ 2 } $
since $y=mx+c$ is parallel to $x+2y=1$
$\therefore { m } _{ 2 }=-\dfrac { 1 }{ 2 } $
also, $y=mx+c\ \Rightarrow \dfrac { -5 }{ 4 } =\dfrac { -1 }{ 2 } .\dfrac { 11 }{ 4 } +c\ \Rightarrow c=\dfrac { 1 }{ 8 } $
therefore equation of line parallel to $x+2y=1$ is given as 
$y=mx+c\ \Rightarrow y=\dfrac { -1 }{ 2 } x+\dfrac { 1 }{ 8 } \ \Rightarrow 4x+8y-1=0$

$2x + y = 0$ is the equation of a diameter of the circle which touches the lines $4x-3y+10=0$ and $4x-3y-30=0$ The center and radius of the circle are ?

  1. $\left (-2, 1\right) ; 4$

  2. $\left (1, -2\right) ; 8$

  3. $\left (1, -2\right) ; 4$

  4. $\left (1, -2\right) ; 16$


Correct Option: C
Explanation:
Given $4x-3y+10=0$ and $4x-3y-30=0$ touches circle implies they are tangent.

Solving the line $2x+y=0$  and  $4x-2y+10=0 $
$x=-1$ and $y=2 $ Point A

Solving the line $2x+y=0$  and  $4x-3y-30=0$
$x=3; y=-6 $ Point B

Distance between the parallel lines is length of diameter
$d=\dfrac{(C _1-C _2)}{\sqrt{(a^2+b^2)}}\\$
$d=\dfrac{(10-(-30)}{\sqrt{(16+9)}}\\$
$d=\dfrac{10+30}{5}$
$d=8$
$r=4$

O is midpoint of AB
$(x,y)=\dfrac{3-1}{2}, \dfrac{2-6}{2}$ $=(1,-2)$

The line $y = x$ meets $y = ke^x , k \le 0$ at

  1. no ponits

  2. one point

  3. two points

  4. none of these


Correct Option: B

Let a, b, c and d be non-zero numbers. If the point of intersection of the lines $4ax+2ay+c=0$ and $5bx+2by+d=0$ lies in the fourth quadrant and is equidistant from the two axes, then:

  1. $2bc-3ad =0$

  2. $2bc+3ad =0$

  3. $3bc -2ad =0$

  4. $3bc +2ad =0$


Correct Option: C
Explanation:

If it lies in the fourth quadrant, we get$(x,-x)$

$2ax+c = 0$ and $3bx+d = 0$
$\cfrac{c}{2a} = \cfrac{d}{3b}$
$3bc-2ad = 0$

If the straight lines joining the origin and the points of intersection of the curve $5{x}^{2}+12y-6{y}^{2}+4x-2y+3=0$ and $x+ky-1=0$ are equally inclined to the $x-axis$, then the value of $k$ is equal to:

  1. $1$

  2. $-1$

  3. $2$

  4. $3$


Correct Option: B

For $a> b> c> 0$, the distance between $(1,1)$ and the point of intersection of the lines $ax+by+c=0$ and $bx+ay+c=0$ is less then $2\sqrt{2}$. Then

  1. $a+b-c> 0$

  2. $a-b+c< 0$

  3. $a-b+c> 0$

  4. $a+b-c< 0$


Correct Option: A

The straight line $mx -y =1+2x$ cuts the circle $x^2 + y^2=1$ at one point at least. Then the set of values of m is

  1. $\left[ -\frac{4}{3}, 0\right]$

  2. $\left[ -\frac{4}{3}, \frac{4}{3}\right]$

  3. $\left[0, \frac{4}{3}\right]$

  4. None of these


Correct Option: A

If $a\neq 0$ and the line $2bx+3cy+4d=0$ passes through the point of intersection of parabolas $y^{2}=4ax$ and $x^{2}=ay$, then

  1. $d^{2}+\left(2b-3c\right)^{2}=0$

  2. $d^{2}+\left(3b-2c\right)^{2}=0$

  3. $d^{2}+\left(2b+3c\right)^{2}=0$

  4. $d^{2}+\left(3b+2c\right)^{2}=0$


Correct Option: A

If the line $y=x$ cuts the curve ${x}^{3}+{3y}^{3}-30xy+72x-55=0$ in points $A,B$ and $C$ then the value of $\dfrac{4\sqrt{2}}{55}$ $OA.OB.OC$ (where $O$ is the origin ), is ?

  1. $55$

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

  3. $2$

  4. $4$


Correct Option: D
Explanation:
${ x }^{ 3 }+3{ y }^{ 3 }-30xy+72x-55=0$
$y=x$
$\Rightarrow { x }^{ 3 }+3{ x }^{ 3 }-30{ x }^{ 2 }+72x-55=0$
$\Rightarrow 4{ x }^{ 3 }-30{ x }^{ 2 }+72x-55=0$
$\Rightarrow x=1.634,-3.367,2.5$
$\therefore A\left( 1.634,1.634 \right) ;B\left( 3.367,3.367 \right) ;C\left( 2.5,2.5 \right) $
$OA=1.634\sqrt { 2 } ,OB=3.367\sqrt { 2 } ,OC=2.5\sqrt { 2 } $
$=\cfrac { 4\sqrt { 2 }  }{ 55 } \times OA\times OB\times OC=4$

Tangent of the angle at which the curve $y=a^{x}$ and $y=b^{x}(a\neq b>0)$ intersect is given by 

  1. $\dfrac{\log ab}{1+\log ab}$

  2. $\dfrac{\log a/b}{1+\left(\log a\right)\left(\log b\right)}$

  3. $\dfrac{\log ab}{1+\left(\log a\right)\left(\log b\right)}$

  4. $none$


Correct Option: A