Q. If the circle $x^2 + y^2 - 6x - 8y + (25 - a^2) = 0$ touches the axis of $x$, then a equals.
Solution:
$x^{2}+y^{2}-6x+8y+\left(25-a^{2}\right)=0$
Radius $=4\sqrt{9+16+\left(25-a^{2}\right)}$
$\Rightarrow a=\pm4$
