(8) Using the formal definition of function, check whether the following subsets of X Y cor-respond to functions of X to Y . Give your reasons why these are or are not functions:(a) f ={(x, y) in X Y x = y4}, where X ={x in R x 0} and Y = R.(b) f ={(x, y) in X Y x2+ y2=1 and y 0},where X = R and Y ={y in R y 0}.