please help, thankyou

Question 3.9 (8 marks) Let a R with fa,b(x) = x - 2 (x E [a, b]) (x * [a, b]). Note: Here the subscripts a, b of fa,b are not partial derivatives, but just subscripts to indicate that the definition of this function depends on these two parameters. Your task is to find out for which a and b the function fab is a PDF of a continuous probability distribu- tion: determine a function g: D - R such that fab is a PDF if and only if a E D and b = g(a). Hint: You may first find the constraint on a, and then obtain b as some function of a