I assume that CE is a tangent to the circle.
If so is an isosceles triangle with base .
Let M be the centre of the circle and CE is tangent to the circle:
4. (CM) is perpendicular bisector of (AB) thus is an isosceles triangle.
6. is an exterior angle.
10.The arc(BC) belongs to the angle . You only have to convert the measure in degree into radians:
Maybe you should seek for the tangent-chord-theorem(?) [I don't know if this is the appropriate name in English] which states that the angle between the chord (here BC, name of angle ) is as large as the angle at the circumference (here ).