Angles in the same segment A & B using same chord CD would always be equal.

It means if the base is taken common to build two triangles on circumference of circle, then angles opposite to base would always be equal.

Angles in the semi-circle are always 90 degree.

It means if the base of triangle is the diameter of circle and its all three vertices are on the circumference of the circle, then the angle made by other two sides opposite to diameter would always be 90 degree

Cyclic Quadrilateral – Any quadrilateral having all its vertices on circumference of circle

The sum of opposite angles in any cyclic quadrilateral would always be 180 degree,

Angle A + Angle C = 180 degree

Angle B + Angle D = 180 degree

The Angle made at center “O” of circle on any segment CD would be twice than any angle “B” made by it on circumference.

Two tangents drawn from a common point to a common circle would be equal always.

AB = AC

Angle made by tangent with a side of triangle is equal to interior opposite angle

As side AB makes angle AEB with Tangent ED, so its interior opposite angle ACB would be equal to angle EAB

Angle EAB = Angle ACB

And Angle CAD = Angle ABC

If center point of the circle is joined through a line with the mid point of any chord, then the line would make 90 degree with the chord

The angle between any radius and tangent would always be 90 degree