Part 2 requires prove that dy/dx will always be negative hence the function will always be decreasing in the given domain ie f(x) decreasing as x increases. Part 3 the “same form” means Rcos(x+a) so solve as you would to find inverse functions. Part 4 quite straight forward since fg means you put whole of g(x) into all x in f(x) so can sub the x in f(x) as g(x) and solve. Use GC find domain.