1)

O(0,0) , A(1,2) , B(3,4)  are the vertices of $\triangle OAB$. The joint equation of the altitude and median drawn from O is 


A) $x^{2}+7xy-y^{2}=0$

B) $x^{2}+7xy+y^{2}=0$

C) $3x^{2}-xy-2y^{2}=0$

D) $3x^{2}+xy-2y^{2}=0$

Answer:

Option D

Explanation:

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 Given , O(0,0) , A(1,2) and  B(3,4) be the vertices of $\triangle $ OAB

Let OP and OD be the altitude and median of $\triangle$ OAB, respectively

 $\therefore$   Coordinates of D= Mid of AB.=  $\left(\frac{1+3}{2},\frac{2+4}{2}\right)=\left(\frac{4}{2},\frac{6}{2}\right)=(2,3)$

 Now, ewquation of OD is (y-0)=  $\left(\frac{3-0}{2-0}\right)(x-0)$

                        $\left[\because y-y_{1}=\left(\frac{y_{2}-y_{1}}{x_{2}-x_{1}}(x-x_{1}\right)\right]$

$\Rightarrow$      $y=\frac{3}{2}x\Rightarrow2y=3x\Rightarrow3x-2y=0$

Slope of Op = -1/ Slope of AB                 $[\because  OP\bot AB]$

                           =$\frac{-1}{\left(\frac{3-1}{4-2}\right)}=\frac{-1}{\frac{2}{2}}=-1$

 $\therefore$ Equation of Op is (y-0) =-1(x-0)

                                             $[\because   y-y_{1}=slope (x-x_{1})]$

$\Rightarrow$     $y=-x\Rightarrow x+y=0$

 Now, joint equation of OP and OD

  (x+y)(3x-2y)=0

 $\Rightarrow$     3x2-2xy+3xy-2y2=0

$\Rightarrow$   $3x^{2}+xy-2y^{2}=0$