Connecting OA and OB

∠∠ACB = 30

∴∠AOB = 60° The central angle of the same arc is equal to twice the circumferential angle.

OA = OB

△ AOB is an equilateral triangle.

∫AB = 1.8cm

∴OA= 1.8cm

∴ circle o diameter = 2 * OA = 3.6cm

5 problems, solutions:

∫AB is the diameter and C is the point on the circumference.

∴∠ACB=90

∫∠BAC = 30

∴ BC =1/2 * ab =1/2 * 8 = 4cm In a right-angled triangle, the right-angled side opposite to 30 is equal to half of the hypotenuse.

∴ AC = √ (AB 2-BC 2) = √ (8 2-4 2) = √ 48 = 4 √ 3 cm Pythagorean theorem