# One-to-one

If f o g are one-to-one, does it follow that g is one-to-one? Justify your answer.

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One-to-one is investigated.

One-To-One Functions

FUNCTIONS

1. Find all functions from X = {a, b, c} to Y = {u, v}.

2. Let F and G be functions from the set of all real numbers to itself. Define new functions F - G: R R and G - F: R R as follows:

(F - G)(x) = F(x) - G(x) for all x R,

(G - F)(x) = G(x) - F(x) for all x R.

Does F - G = G - F? Explain.

3. Let A = {2, 3, 5} and B = {x, y}. Let p1 and p2 be the projections of AB onto the first and second coordinates. That is, for each pair (a, b) AB, p1(a, b) = a and p2(a, b) = b.

Find p2(2, y) and p2(5, x). What is the range of p2?

4. Let X = {1, 5, 9} and Y = { 3, 4, 7}. Define g : XY by specifying that g(1) = 7, g(5) = 3, g(9) = 4.

Is g one-to-one? Is g onto? Explain your answers.

5. Let X = {1, 2, 3}, Y = {1, 2, 3, 4}, and Z = {1, 2}.

a) Define a function g : X Z that is onto but not one-to-one.

b) Define a function k : X X that is one-to-one and onto but is not the identity function on X.

6. Let X = {1, 2, 3, 4}, Y = {2, 3, 4, 5, 6}, Z = {1, 2, 3}.

a) Define a function f: X Y that is one-to-one but not onto.

b) Define a function g: X Z that is onto but not one-to-one.

c) Define a function h: X Y that is neither onto nor one-to-one.

d) Define a function k: X X that is onto and one-to-one but is not the identity function on X.

7. List all the functions from the three element set {1, 2, 3} to the set {a, b}. Which functions, if any, are one-to-one? Which functions, if any, are onto?

8. Define f: R R by the rule f(x) = 2x2-3x+1

a) Is f one-to-one? Prove or give a counterexample.

b) Is f onto? Prove or give a counterexample.

9. Define g : Z Z by the rule g(n) = 3n - 2, for all integers n.

a) Is g one-to-one? Prove or give a counterexample.

b) Is g onto? Prove or give a counterexample.

10. Let X = {a, b, c, d, e} and Y = {s, t, u, v, w}. A one-to-one correspondence F: XY is defined by: F(a) = t, F(b) = w, F(c) = s, F(d) = u, F(e) = v. Define F-1 (Please, specify each function value, i.e. F-1(s) = ...what-ever, or draw the diagram).

11. Give a real-world example of a function which is both one to one and onto