Question

ONLY GENIUS CAN ANSWER.....100 POINTS ...

Answer 1

AB is the radius here....
But without any measurements I can't tell the length of AB.
So your question seems incomplete

Answer 2

Measure of AB is 90 because the measure of a circle is 360 and measure of half circle is 180 and half of 180 is 90. (I am not sure about my answer.