The radical axis of the circles
\[
x^2+y^2+4x+6y+7=0
\]
and
\[
4x^2+4y^2+8x+12y-24=0
\]
is a tangent to the circle
\[
x^2+y^2=13
\]
at a point \((\alpha,\beta)\), then \(\alpha+\beta=\)
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The point of contact of a tangent to the circle
\[
x^2+y^2=r^2
\]
lies on the radius perpendicular to the tangent line. The radius vector is parallel to the normal vector of the tangent.