about circlesthis theorum:-
Your Question was
"if a chord is drawn through the point of contact of a tangent to a circl then the angles which this chord makes with the given tangent are equal resp.to the angles formed in the corresponding alternate segments."
This is the alternate segment theorem which is not a part of CBSE class X this year.
However it can be be explained using the two results angles in the same segment are equal and opposite angles of the triangle are supplementary.