Finding the domain and range of a quadratic function
Find the domain and range of
As with any quadratic function, the domain is all real numbers.
Because
is negative, the parabola opens downward and has a maximum value. We need to determine the maximum value. We can begin by finding the
value of the vertex.
Determining the maximum and minimum values of quadratic functions
The output of the quadratic function at the vertex is the maximum or minimum value of the function, depending on the orientation of the
parabola . We can see the maximum and minimum values in
[link] .
There are many real-world scenarios that involve finding the maximum or minimum value of a quadratic function, such as applications involving area and revenue.
Finding the maximum value of a quadratic function
A backyard farmer wants to enclose a rectangular space for a new garden within her fenced backyard. She has purchased 80 feet of wire fencing to enclose three sides, and she will use a section of the backyard fence as the fourth side.
Find a formula for the area enclosed by the fence if the sides of fencing perpendicular to the existing fence have length
What dimensions should she make her garden to maximize the enclosed area?
Let’s use a diagram such as
[link] to record the given information. It is also helpful to introduce a temporary variable,
to represent the width of the garden and the length of the fence section parallel to the backyard fence.
We know we have only 80 feet of fence available, and
or more simply,
This allows us to represent the width,
in terms of
Now we are ready to write an equation for the area the fence encloses. We know the area of a rectangle is length multiplied by width, so
This formula represents the area of the fence in terms of the variable length
The function, written in general form, is
The quadratic has a negative leading coefficient, so the graph will open downward, and the vertex will be the maximum value for the area. In finding the vertex, we must be careful because the equation is not written in standard polynomial form with decreasing powers. This is why we rewrote the function in general form above. Since
is the coefficient of the squared term,
and
To find the vertex:
The maximum value of the function is an area of 800 square feet, which occurs when
feet. When the shorter sides are 20 feet, there is 40 feet of fencing left for the longer side. To maximize the area, she should enclose the garden so the two shorter sides have length 20 feet and the longer side parallel to the existing fence has length 40 feet.
Given an application involving revenue, use a quadratic equation to find the maximum.
Write a quadratic equation for a revenue function.
Find the vertex of the quadratic equation.
Determine the
y -value of the vertex.
Questions & Answers
If c is the cost function for a particular product, find the marginal cost functions and their
values at x=10 a. c(x) = 800+ 0.04x + 0.0002x² b. c(x) = 250 + 100x + 0.001x²
when you reduce an equation to its simplest terms, you can't change the value of the equation. reducing it to y + 5 is equivalent to dividing it by 9 which changes the value. you can multiply it by 1 or 9/9 which would give 9(y + 5). multiplying it by one does not change the value.
Philip
Given a polynomial expression, factor out the greatest common factor.
The denominator of a certain fraction is 9 more than the numerator. If 6 is added to both terms of the
fraction, the value of the fraction becomes 2/3. Find the original fraction.
2. The sum of the least and greatest of 3 consecutive integers is 60. What are the valu
Q2
x+(x+2)+(x+4)=60
3x+6=60
3x+6-6=60-6
3x=54
3x/3=54/3
x=18
:. The numbers are 18,20 and 22
Naagmenkoma
Mark and Don are planning to sell each of their marble collections at a garage sale. If Don has 1 more than 3 times the number of marbles Mark has, how many does each boy have to sell if the total number of marbles is 113?