Proving algebraic equations with circle theorems 
I got as far as stating that OBP=90˚ (as angle between tangent and radius is always 90˚), and thus CBO=90˚- 2x. CBO=OCB as they are bases in a isosceles. COB=180-90-2x-90-2x. But after this, i am clueless.
I am stuck with this Question. It is from a GCSE Further Maths past paper. Despite seeing online tutorials, and checking the answer scheme, I still don't understand how you solve this question. Could you please show me a step by step explanation of how you solve this question. Thank you.


ANSWER:


Angle BOD = 180 − y
Angle OCD = x
Angle OBC = 90 − 2x
Angle BCO= 90 − 2x
Angle BOD reflex = 360 - (90 − 2x) − (90 − 2x) − x − x = 180 + 2x.
180 − y + 180 + 2x = 360, 
thus  y = 2x
