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# one-to-one function

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(a) Define the function f: R-->R by f(x) = x3 + 4. Briefly explain why f is a 1-1 (one-to-one) function. No proof necessary, just
an explanation in some detail (b) Is the function g: R -->Z defined by g(n) = [n/2]a one to one function?
(Be careful,[n/2]means the ceiling function.) Explain. (c) Briefly explain what f-1 means in general and then find f-1for the function f
in part a.

https://brainmass.com/math/discrete-structures/one-to-one-function-409564

#### Solution Preview

(a) One way to determine that f(x) is a one-to-one function is to graph the function. The graph of f(x) is the graph of y=x^3 shifted up 4 units. This function passes the horizontal line test. That is, any horizontal line that we can ...

#### Solution Summary

One-to-one functions are examined.

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## 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 AB onto the first and second coordinates. That is, for each pair (a, b)  AB, 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 : XY by specifying that g(1) = 7, g(5) = 3, g(9) = 4.
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: XY 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

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