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Example Questions
Example Question #21 : How To Find The Domain Of A Function
Define a function , restricting the domain to the interval .
Give the range of .
A quadratic function has a parabola as its graph; this graph decreases, then increases (or vice versa), with a vertex at which the change takes place.
The -coordinate of the vertex of the parabola of the function
is .
The -coordinate of the vertex of the parabola of can be found by setting :
.
, so the vertex is not within the interval to which the domain is restricted. Therefore, increases or decreases constantly on , and its maximum and minimum on this interval will be found on the endpoints. These values are and , which can be evaluated using substitution:
The range is .
Example Question #22 : How To Find The Domain Of A Function
Define a function , restricting the domain to the interval .
Give the range of .
A quadratic function has a parabola as its graph; this graph changes direction at a vertex.
The -coordinate of the vertex of the parabola of the function
is .
The -coordinate of the vertex of the parabola of can be found by setting :
, so the vertex is not on the domain. The maximum and the minimum of must occur at the endpoints, so evaluate and .
The minimum and maximum values of are and 40, respectively, so the correct range is .
Example Question #23 : How To Find The Domain Of A Function
Define a function , restricting the domain to the interval .
Give the range of .
A quadratic function has a parabola as its graph; this graph changes direction at a vertex.
The -coordinate of the vertex of the parabola of the function
is .
The -coordinate of the vertex of the parabola of can be found by setting :
, so the vertex is on the domain. The maximum and the minimum of must occur at the vertex and one endpoint, so evaluate , , and .
The minimum and maximum values of are and 17, respectively, so the correct range is .
Example Question #21 : How To Find The Domain Of A Function
Define , restricting the domain of the function to .
Determine (you need not determine its domain restriction).
does not exist
First, we must determine whether exists.
A quadratic function has a parabola as its graph; this graph changes direction at its vertex.
exists if and only if, if , then - or, equivalently, if there does not exist and such that , but . This will happen on any interval on which the graph of constantly increases or constantly decreases, but if the graph changes direction on an interval, there will be such that on this interval. The key is therefore to determine whether the interval to which the domain is restricted contains the vertex.
The -coordinate of the vertex of the parabola of the function
is .
The -coordinate of the vertex of the parabola of can be found by setting :
.
The vertex of the graph of without its domain restriction is at the point with -coordinate . Since , the vertex is not in the interior of the domain; as a consequence, exists on .
To determine the inverse of , first, rewrite in vertex form
, the same as in the standard form.
The graph of , if unrestricted, would have -coordinate , and -coordinate
Therefore, .
The vertex form of is therefore
Replace with :
Switch and :
Solve for . First, add 46 to both sides:
Multiply both sides by 2:
Take the square root of both sides:
Subtract 8 from both sides
Replace with :
Either or
The domain of is the set of nonnegative numbers; this is consequently the range of . can only have negative values, so the only possible choice for is .
Example Question #21 : Algebraic Functions
Define a function , restricting the domain to the set of nonnegative real numbers.
Give the range of .
A quadratic function has a parabola as its graph; this graph changes direction at its vertex.
The -coordinate of the vertex of the parabola of the function
is .
The -coordinate of the vertex of the parabola of can be found by setting and :
.
Since , the vertex falls within the domain of .
Since, in , the quadratic coefficient is positive, the parabola curves upward. On the set of all nonnegative numbers, the function has no maximum. The minimum occurs at the vertex, which is in the domain; to calculate it, evaluate :
The range of the function given the domain restriction is .
Example Question #21 : Algebraic Functions
Define a function .
It is desired that is domain be restricted so that have an inverse. Which of these domain restrictions would not achieve that goal?
A quadratic function has a parabola as its graph; this graph changes direction at its vertex.
exists if and only if, if , then - or, equivalently, if there does not exist and such that , but . This will happen on any interval on which the graph of constantly increases or constantly decreases, but if the graph changes direction on an interval, there will be such that on this interval. The key is therefore to identify the interval that contains the vertex.
The -coordinate of the vertex of the parabola of the function
is .
The -coordinate of the vertex of the parabola of can be found by setting :
.
Of the five intervals among the choices,
so cannot exist if is restricted to this interval. This is the correct choice.
Example Question #24 : How To Find The Domain Of A Function
Define .
It is desired that is domain be restricted so that have an inverse. Which of these domain restrictions would not achieve that objective?
has an inverse regardless of the domain
is an absolute value of a linear expression; as such, its graph is a "V" shape whose vertex occurs at the point at which .
exists if and only if, if , then - or, equivalently, if there does not exist and such that , but . This will happen on any interval on which the graph of constantly increases or constantly decreases, but if the graph changes direction on an interval, there will be such that on this interval. The key is therefore to identify the interval that contains the vertex.
Set
and solve for :
Of the four intervals in the choices,
,
so cannot exist if is restricted to this interval. This is the correct choice.
Example Question #22 : How To Find The Domain Of A Function
Define a function , restricting the domain to . Give the range of .
Consider the function . Then
.
is an absolute value of a linear function. Since the value of this function cannot be less than 0, its graph changes direction at the value of at which
This value can be found by solving for :
, so the change of direction does not occur on the domain - it increases everywhere or decreases everywhere, so, if restricted to the given domain, we can treat this as if it were a simple linear function. Consequently, we can find the minimum and maximum at the endpoints. Evaluating and :
This makes the range of on the given domain.
Example Question #21 : How To Find The Domain Of A Function
Find the domain of the function.
All Real Numbers
In order to find the domain of a function, you need to state for what values of x the function can be true. The trick to finding the domain is to figure out what the value of x cannot be, and adjusting your answer appropriately.
In the function, , it is clear that x cannot be equal to 5. If x was 5, there would be a zero in the denominator, which would cause the function to be undefined. Remember, you can never have a zero in the denominator! That is the main thing to look out for when being asked for the domain of a function.
All other values for x are acceptable, so your answer is that x can be anything other than 5.
The proper way to write that x is any value other than 5 is,
which states that the domain can be all numbers from negative infinity to positive infinity, excluding 5.
Example Question #26 : How To Find The Domain Of A Function
Define a function , restricting the domain to . Give the range of .
Consider the function . Then
.
This is an absolute value function. Since the value of this function cannot be less than 0, its graph changes direction at the value of at which . This value can be found by setting
and solving for :
, so assumes the value 0 on this domain. This must be the minimum value.
A function of the form is a linear function and is either constantly increasing or constantly decreasing. Therefore, constantly increases on one side and decreases on the other. Therefore, the maximum must occur at either endpoint of the domain of . Evaluate both and :
13, the greater of the two values, is the maximum value. The range of on the given domain is .
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