the ordered pair 1,5 belongs to a function f, explain why the ordered pair 2,1 can't belong to f^-1
If the ordered pair `(1,5)` belongs to f, then the ordered pair (5,1) belongs to its inverse. (The inverse of a relation consisting of points of the form (x,y) is the set of points (y,x) )
If (2,1) was on the inverse, then the function contains (1,2). But since this is a function, f cannot have both (1,5) and (1,2) so (2,1) cannot belong to f's inverse.