#1**+1 **

Arc ACB is half the circle. The whole circle is 360^{o} so ACB is 180^{o}

Arc AC is given as 100^{o} which leaves 80^{o} for arc CB

There's a relationship between the size of an angle subtended by an arc of a circle.

When the angle's vertex lies on the circle the size of the angle is equal to half the arc.

So angle CAB is **40 ^{o}**

BTW, when the angle's vertex lies on the center of the circle, the arc and the angle are the same amount of degrees.

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Guest Aug 12, 2020

edited by
Guest
Aug 12, 2020