Functions in Mathematics

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Questions and Answers

What is the output of the function f when the input is 2, given that f(x) = 6x + 28?

  • 36
  • 44
  • 28
  • 40 (correct)

What does the floor function ⌊x⌋ return when x is a real number?

  • The smallest integer greater than x
  • The next integer after x
  • The largest integer less than or equal to x (correct)
  • The integer part of x without rounding

Which function defines g(n) based on whether n is odd or even?

  • g(n) = n + 1
  • g(n) = 3n + 4
  • g(n) = 2n + 3
  • g(n) = 2n or 3n^2 + n + 1 (correct)

For the function â„“(E) defined for healthy African elephants, what does â„“(E) represent?

<p>The left ear of an elephant (B)</p> Signup and view all the answers

What is the output of g(4), given that g(n) is defined for odd and even n?

<p>53 (A)</p> Signup and view all the answers

What is the result of applying the floor function to the number -32?

<p>-2 (B)</p> Signup and view all the answers

If n is odd and g(n) = 2n, what is g(3)?

<p>6 (B)</p> Signup and view all the answers

If the output of f(0) is 28, what term in the formula contributes to this result?

<p>28 (A)</p> Signup and view all the answers

What does the ceiling function ⌈x⌉ return for a real number x?

<p>The smallest integer greater than or equal to x (D)</p> Signup and view all the answers

If x = -54, what is the value of the ceiling function ⌈x⌉?

<p>-53 (A)</p> Signup and view all the answers

Which of the following correctly describes arity in functions?

<p>The number of inputs a function can take (D)</p> Signup and view all the answers

What term is used to describe a function with two arguments?

<p>Binary function (C)</p> Signup and view all the answers

What is the definition of a function from set A to set B?

<p>A function associates each element of A with exactly one element of B. (B)</p> Signup and view all the answers

Given the binary function f(x,y) = x + y, which of the following is an equivalent expression?

<p>xf y = z where z is the result of the addition (C)</p> Signup and view all the answers

Which of the following represents the proper notation of a function?

<p>f : A → B (B)</p> Signup and view all the answers

How can a tuple be thought of in terms of functions?

<p>As a function mapping each index to its corresponding value (D)</p> Signup and view all the answers

In the context of functions, what can be said about the domain?

<p>Every element in the domain must be mapped to some element in the codomain. (B)</p> Signup and view all the answers

For the infinite sequence (b0, b1, b2,...), how is it represented as a function?

<p>f: N → S where f(n) = bn (C)</p> Signup and view all the answers

Why is the relation f(x) as 'parent of x' not considered a function?

<p>A person may have more than one parent. (C)</p> Signup and view all the answers

Which of the following is true about the function f(x) = 'mother of x'?

<p>It associates every human to a unique mother. (B)</p> Signup and view all the answers

What is the relationship between the ceiling function and the floor function?

<p>The floor of a negative number is the negative ceiling of that number. (D)</p> Signup and view all the answers

What characterizes the function f(x) = 'set of all children of x'?

<p>It is a function but not a H → H function. (D)</p> Signup and view all the answers

If you define f : A → B where A = {a, b, c} and B = {1, 2, 3}, what could be a possible description of the function?

<p>f(a) = 1, f(b) = 1, f(c) = 3 (C)</p> Signup and view all the answers

How many distinct outputs can a single input have in a valid function?

<p>Exactly one output. (B)</p> Signup and view all the answers

What is the relationship between the set of natural numbers N and its power set P(N)?

<p>N is countable but P(N) is not (B)</p> Signup and view all the answers

What can be concluded from the set Df defined in the content?

<p>Df does not belong to the range of f. (C)</p> Signup and view all the answers

What does the existence of the subset Df imply about any function f: N → P(N)?

<p>f cannot cover all subsets of N. (C)</p> Signup and view all the answers

If n ∈ Df, which of the following must be true?

<p>n is not included in f(n). (D)</p> Signup and view all the answers

What does the term 'onto' refer to in the context of functions?

<p>A function where every element in the codomain has a preimage in the domain. (C)</p> Signup and view all the answers

What is the recurrence relation for the sequence defined in the basis step?

<p>f(n) = f(n - 2) + f(n - 1) (D)</p> Signup and view all the answers

Which of the following correctly represents the composition of the functions f and g?

<p>(f â—¦ g)(a) = f(g(a)) (B)</p> Signup and view all the answers

For the functions f and g defined where g: X → X and f: X → Y, which outcome is correct for (f ◦ g)(c)?

<p>1 (D)</p> Signup and view all the answers

What happens when trying to compute (f â—¦ f) or (g â—¦ f)?

<p>They are not defined. (C)</p> Signup and view all the answers

Given the functions f(x) = 2x + 3 and g(x) = 3x + 2, what is the result of (g â—¦ f)(x)?

<p>6x + 11 (D)</p> Signup and view all the answers

Which sequence does the Fibonacci function f(n) follow based on the provided pattern?

<p>1, 1, 2, 3, 5, 8, 13 (A)</p> Signup and view all the answers

In the function definitions, which statement about the codomain and domain is correct?

<p>The codomain of g must equal the domain of f for successful composition. (C)</p> Signup and view all the answers

Given the recursive definition, what is the value of f(5)?

<p>8 (C)</p> Signup and view all the answers

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Study Notes

Functions

  • A function from set A to set B associates each element of A with exactly one element of B
  • If f associates x ∈ A with y ∈ B, we write f(x) = y, meaning "f of x is y"
  • f: A → B, where A is the domain and B is the codomain
  • Every element in the domain must have a corresponding element in the codomain, but not every element in the codomain needs to be mapped

Describing Functions

  • Functions can be described by listing associations, drawing points and arrows, or using a graph
  • Functions can be defined using formulas, case distinctions, or by non-formulaic rules

Useful Functions

  • The floor function, ⌊ ⌋ : R → Z, gives the largest integer less than or equal to its input
  • The ceiling function, ⌈ ⌉ : R → Z, gives the smallest integer greater than or equal to its input

Multiple Argument Functions

  • Functions can have multiple arguments, denoted by f(x1,...,xn)
  • Binary functions have two arguments and can use infix notation (xf y = z)

Tuples and Sequences as Functions

  • A tuple (a1, a2,..., an) can be seen as a function mapping {0, 1,...,n-1} to the elements of the tuple
  • An infinite sequence (b0, b1,...) can be seen as a function mapping N to the sequence elements

Function Composition

  • The composition of g: A → B and f: B → C is f â—¦ g: A → C, defined by (f â—¦ g)(a) = f(g(a))
  • Composition is only defined when the codomain of g matches the domain of f

Countability

  • A set is countable if its elements can be put into a one-to-one correspondence with the natural numbers
  • The set of natural numbers itself is countable
  • Not all sets are countable, such as the power set P(N) – the set of all subsets of N

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