Answer:
<ABC =
(The central angle of a circle is twice any inscribed angle subtended by the same arc).
Step-by-step explanation:
From the diagram, ABC is an inscribed isosceles triangle. But the radius of the circle equals the length AC.
Join P to A and C to form an equilateral triangle. An equilateral triangle has equal sides and angles. So, the value of each interior angle of the equilateral triangle is;
Sum of angle in a triangle = 
So that each interior angle = 
= 
The value of each interior angle of the triangle is
. Thus, <APC =
.
⇒ <ABC =
(The central angle of a circle is twice any inscribed angle subtended by the same arc.)