Can somebody showed me a worked solution to the question 12a which is attached to this post?
Worked solutions are not allowed on TSR. I encourage you to think of what you have, how you can use the symmetry of the curve and how you can set up equations.
I've just tried the question and I didn't get sigma to be 8, it's been a while since I did S1 so I may be wrong but I think the question is wrong. Can anyone who's more familiar with S1 double check?