Question

The equation of the circle concentric with $x^2+y^2+6x+2y+1=0$ and passing through the point (-2, -1) is

• A. $x^2+y^2+4x+2y+5=0$
• B. $x^2+y^2+4x+2y+6=0$
• C. $x^2+y^2+6x+2y+6=0$
• D. $x^2+y^2+6x+2y+9=0$

Answer 1

Answer: (D)

$x^2+y^2+6x+2y+1=0$
Centre of this circle is (-3, -1)
Radius of the circle having centre at (-3, -1) and passing through the point (-2, -1) is given by
$r=\sqrt{{\left(-3+2\right)}^2+{\left(-1+1\right)}^2}=1$
$\therefore$ Equation of circle is ${\left(x+3\right)}^2+{\left(y+1\right)}^2=1$
$\Rightarrow x^2+y^2+6x+2y+9=0$.