In a plane the circles
and
with centers
and
, respectively, intersect in two points
and
. Assume that
is obtuse. The tangent to
in
intersects
again in
and the tangent to
in
intersects
again in
. Let
be the circumcircle of the triangle
. Let
be the midpoint of that arc
of
that contains
. The lines
and
intersect
again in
and
, respectively. Prove that the line
is perpendicular to
.
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In a plane the circles $\mathcal K_1$ and $\mathcal K_2$ with centers $I_1$ and $I_2$, respectively, intersect in two points $A$ and $B$. Assume that $\angle I_1AI_2$ is obtuse. The tangent to $\mathcal K_1$ in $A$ intersects $\mathcal K_2$ again in $C$ and the tangent to $\mathcal K_2$ in $A$ intersects $\mathcal K_1$ again in $D$. Let $\mathcal K_3$ be the circumcircle of the triangle $BCD$. Let $E$ be the midpoint of that arc $CD$ of $\mathcal K_3$ that contains $B$. The lines $AC$ and $AD$ intersect $\mathcal K_3$ again in $K$ and $L$, respectively. Prove that the line $AE$ is perpendicular to $KL$.