Question

If the circle $x^2+y^2-6x-8y+(25-a^2)=0$ touches the axis of $x$, then a equals.

• A. $0$
• B. $\pm 4$
• C. $\pm 5$
• D. $\pm 6$

Answer 1

Answer: (B)

$x^2+y^2-6x+8y+\left(25-a^2\right)=0$
Radius $=4\sqrt{9+16+\left(25-a^2\right)}$
$\Rightarrow a=\pm 4$