Question

A circle is drawn touching the $x$-axis and centre at the point which is the reflection of $( a , b )$ in the line $y-x=0$. The equation of the circle is -

• A. $x^2+y^2-2 b x-2 a y+a^2=0$
• B. $x^2+y^2-2 b x-2 a y+b^2=0$
• C. $x^2+y^2-2 a x-2 b y+b^2=0$
• D. $x ^2+ y ^2-2 ax -2 by + a ^2=0$

Answer 1

Answer: (B)

Reflection of point $( a , b )$ on the line
$y=x$ will be $(b, a)$
$(x-b)^2+(y-a)^2=a^2$
$x^2+y^2-2 b x-2 a y+b^2=0$