In the given figure we have that
AC=AD -----> by the radius of the circle
Δ ACO -------> is a right triangle
Δ ADO -------> is a right triangle
Applying the Pythagorean Theorem in both triangles
AC^2=CO^2+AO^2
AD^2=DO^2+AO^2
Remember that
AC=AD ----> radius of the circle
so
CO=DO
Δ ACO≅Δ ADO -----> by SSS
therefore
is proved that the radius that bisects the chord is a perpendicular bisector
