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

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Professor PC Thomas Classes · Answer

If circle touches x-axis, $g^2 = c \implies (-3)^2 = 25-a^2 \implies 9 = 25-a^2 \implies a^2 = 16 \implies a = \pm 4$.