Prove that the angle subtended by an arc at the centre (2b) is twice the angle subtended at the circumference (b).
Hint: Draw a line from the centre o, to the point where the two lines cross the circumference at the top of the diagram
Draw a line, one radius long to split the triangle into two isosceles triangles as shown
Mark the angles b and c for each isosceles triangles.
Work out the other angles in each triangle
Work out the angle left at the centre. 360° – (180°–2b) – (180°–2c) = 2(b+c)
i.e. twice the angle at the circumference
Find the value of x