F(x) = x^2

Definition

The function f(x) = x^2 is a mathematical expression that describes a quadratic function, where the output value is the square of the input value. This function takes any real number x and returns a non-negative value, representing a parabolic curve when graphed. Understanding this function is crucial for analyzing various types of functions, particularly in determining their characteristics such as injectiveness, surjectiveness, and bijectiveness.

5 Must Know Facts For Your Next Test

1. The function f(x) = x^2 is not injective because both positive and negative inputs yield the same output; for instance, f(2) = 4 and f(-2) = 4.
2. It is not surjective when considering the set of all real numbers as its codomain since it cannot produce negative outputs.
3. When graphed, f(x) = x^2 creates a parabola that opens upwards with its vertex at the origin (0,0).
4. To be bijective, a function must be both injective and surjective; since f(x) = x^2 fails to meet these criteria, it is not bijective.
5. The function f(x) = x^2 can be restricted to a domain of non-negative numbers to achieve injectiveness by limiting the inputs to [0, ∞).

Review Questions

• What characteristics make f(x) = x^2 non-injective, and how does this affect its graph?
  • The function f(x) = x^2 is non-injective because it maps both positive and negative values of x to the same output. For example, f(3) = 9 and f(-3) = 9 demonstrate that different inputs produce identical outputs. This results in a parabolic graph that does not have a horizontal line test, indicating that it fails to satisfy the conditions of an injective function.
• Discuss how restricting the domain of f(x) = x^2 could lead to injectiveness and why this is significant.
  • By restricting the domain of f(x) = x^2 to non-negative numbers (i.e., [0, ∞)), the function becomes injective since each input now produces a unique output. This restriction is significant because it allows for one-to-one mapping between elements in the domain and range. This means that one can confidently say that every y-value corresponds to only one x-value, thus enabling the possibility of defining an inverse function over this limited domain.
• Evaluate how understanding the properties of f(x) = x^2 contributes to recognizing bijective functions in broader mathematical contexts.
  • Understanding f(x) = x^2 helps clarify the distinction between different types of functions like injective, surjective, and bijective. By analyzing this quadratic function, one can see why it fails to be bijective due to its non-injectiveness and lack of surjectiveness over real numbers. Recognizing these properties allows for deeper comprehension of how bijective functions operate within other mathematical constructs, emphasizing their importance in areas such as inverse functions and one-to-one correspondences in set theory.

Related terms

Quadratic Function: A polynomial function of degree two, typically expressed in the form f(x) = ax^2 + bx + c, where a, b, and c are constants.

Injective Function:

A function where each element of the range is mapped by exactly one element of the domain, meaning no two inputs produce the same output.

Bijective Function:

A function that is both injective and surjective, establishing a one-to-one correspondence between elements of the domain and range.