Provide a specific value of x where two (or more) values of y can be assigned

Question

Provide a specific value of x where two (or more) values of y can be assigned for these two examples which are not functions:

a) x²+y²=4

b) siny=x

Answer 1

y=±sqrt(4-x²)

y=arcsin x

From these two "hints" you should be able to pick values for x as required.