Let
be a convex quadrilateral with the line
being tangent to the circle on diameter
. Prove that the line
is tangent to the circle on diameter
if and only if the lines
and
are parallel.
%V0
Let $ABCD$ be a convex quadrilateral with the line $CD$ being tangent to the circle on diameter $AB$. Prove that the line $AB$ is tangent to the circle on diameter $CD$ if and only if the lines $BC$ and $AD$ are parallel.
Školjka