In the diagram attached a is the centre ogf the circle (O doesn't work in paint).
P,Q,R and S are points on the circle
Angle ROP = 110
Calculate the angle RSP
I Don't know how to prove it is a parallelogram (if it is (although I suspect it is)), I need names of laws and if there are specific names given to various angles (not like obtuse or acute but things like RSP is the intercept angle, although I know it's not but I don't know what the intercept angle is)
This is all GCSE standard, please do not venture further.