ABCD are points on the circumference of a circle centre 0. Angle BCD = 130°
Angle ABC = 105°
Angle OBC = Angle ODC
А
Not drawn
accurately
105
130
с
Work out the size of angle ADO marked c on the diagram.
(4 marks)

1. ∠1 is complementary to ∠2 and ∠3 is complementary to ∠2. subtraction property of equality 2. m∠1 + m∠2 = 90 and m∠3 + m∠2 = 90 substitution 3. m∠1 + m∠2 = m∠3 + m∠2 definition of complementary 4. m∠1 = m∠3 given