What is the Range of a Function with Rule F(x) = x^2 - 1 on the Interval [-2,5]?

In summary, the function F(x) = x^2 - 1 has a range of [-1,24]. The lower bound of -1 can be obtained by plugging in the maximum value in the domain, 5, into the function and subtracting 1. The graph of the function can also show this, but the range can also be proven using the definitions of set equality and range of a function. To find the minimum value, one can use the endpoints of the interval and look at where the derivative of the function equals 0. It is important to consider all methods, including using a graph, to fully understand the function.
  • #1
cue928
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Let F: [-2,5] --> R be function with rule F(x) = x^2 - 1. Show range of F = [-1,24].

I get that 5^2 = 25 - 1 = 24, but how does one get the lower bound of the range to be -1?
 
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  • #2
cue928 said:
Let F: [-2,5] --> R be function with rule F(x) = x^2 - 1. Show range of F = [-1,24].

I get that 5^2 = 25 - 1 = 24, but how does one get the lower bound of the range to be -1?
52 [itex]\neq[/itex] 24, but F(5) = 52 - 1 = 24.

Sketch a graph of the function and you should be able to see why the minimum value in the range is -1.
 
  • #3
Understood but unfortunately I can't use the graph to show it. They want us to use the definition of set equality and range of a function to do it.

I understand that for two sets to be equal, A must be a subset of B and B must be a subset of A. For range of a function f from A to be, y is an element of B such for all x in A, x,y must both be elements of F. But I'm not making the connection between the two definitions and the question.
 
  • #4
To test for maxima and minima, you look at the two points onthe end of the interval (-2 and 5 in this case), then look at where F'(x) = 0.
 
  • #5
How do you find the minimum of a function?
 
  • #6
cue928 said:
Understood but unfortunately I can't use the graph to show it. They want us to use the definition of set equality and range of a function to do it.
Just because you can't use a graph to show what you need to show, that's not a good reason to skip that step. A graph might help you understand the function you're working with. Your function describes a portion of a very simple geometric figure. It's not clear to me that you realize this.
 

FAQ: What is the Range of a Function with Rule F(x) = x^2 - 1 on the Interval [-2,5]?

What is a function?

A function is a mathematical relationship between two sets of numbers, where each input has exactly one output. It can also be thought of as a rule that assigns each input value to a unique output value.

How do you prove that a relationship is a function?

To prove that a relationship is a function, you must show that each input value has exactly one corresponding output value. This can be done by creating a table or graph of the relationship and checking that no input values have multiple output values. Another way is to use the vertical line test, where a vertical line is drawn through the graph and it should only intersect at one point for each input value.

What is a function's domain?

A function's domain is the set of all possible input values for which the function is defined. It is often represented by the letter 'x' and can be numbers, variables, or other mathematical expressions.

What is a function's range?

A function's range is the set of all possible output values for the function. It is often represented by the letter 'y' and can be numbers, variables, or other mathematical expressions.

How do you find the range of a function?

To find the range of a function, you can either create a table or graph of the function and list all the output values, or you can use algebraic methods such as finding the maximum and minimum values of the function. Additionally, if the function is given in equation form, you can use substitution to find specific output values.

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