Answer:
Step-by-step explanation:
Remark
Triangle BAC is isosceles. It has 2 sides that are both radii of the circle. I assume that C is the center of the circle.
Givens
AC = BC Both of these are radii.
<BCD = 20o Given
<A and <B are equal Both are opposite a radii of the circle
C is the circle's center Assumed otherwise we can't do it.
Solution
<BCD is an exterior angle of Triangle ACB It's on the same straight line as D and A
The sum of 2 remote interior angles = the sum of the exterior angle.
BAC = ABC Stated above
BAC + ABC = 20 Stated right above.
2BAD = 20
BAD = 20/2
BAD = 10
