Angle at the centre of a circle theorem

What circle theorem can be used in this diagram?

• A 90-degree angle is formed in a semi-circle

• The angle at the centre of a circle is twice the angle at the circumference

• Angles in a cyclic quadrilateral add to make 180 degrees

• Alternate segment theorem

Find the value of the angle marked x....

• 50

• 100

• 80

• 90

What is the m∠ADB?

• 16^o
• 32^o
• 64^o
• 14^o

find the measure of angle a

• 30
• 21
• 60
• 120

Find the value of the angle marked x....

• 125

• 70

• 110

• 55

Shown is a circle with centre O.

ABC is a straight line.

Angle CBD is 146°.

Find the size of angle AOD.

• 86

• 68

• 34

What are the sizes of a and b?

• a = 57, b = 114

• a = 57, b = 57

• a = 114, b = 57

• a = 57, b = 28.5