Question

The equation of the radical axis of the two circles $7x^2+7y^2-7x+14y+18=0$ and $4x^2+4y^2-7x+8y+20=0$ is given by

• A. $3x^2+3y^2-6y-2=0$
• B. $21x-68=0$
• C. $x-2y-5=0$
• D. $x+2y+5=0$

Answer 1

The correct option is B $21x-68=0$

So, $e{q}^n$ of radial axis of circle is given by $s_1-s_2=0$
$s_1=x^2+y^2-x+2y+\frac{18}{7}=0$
$s_2=x^2+y^2-\frac{7x}{4}+y+5=0$
$\therefore s_1-s_2=0$
$\Rightarrow \frac{3x}{4}-\frac{17}{7}=0$
$\Rightarrow 21x-68=0$