# Section 8.4 Quadratic Functions.

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Section 8.4 Quadratic Functions

8.4 Lecture Guide: Quadratic Functions
Objective 1: Distinguish between linear and quadratic functions. A second-degree polynomial function can be written in the form and is called a quadratic function.

First Degree Functions --- Linear Functions
Algebraically: Numerically: Graphically: A fixed change in x produces a constant change in y. A straight line Example:

Second Degree Functions --- Quadratic Functions
Algebraically: Numerically: Graphically: The y-values from a symmetric pattern about the vertex. A parabola Example:

1. For a linear function in the form the graph will slope upward to the right if __________________ and the graph will slope downward to the right if ________________. 2. For quadratic functions in the form the graph will open up if _________________ and the graph will open down if __________________.

Identify the graph of each function as a line or a parabola. If
the graph is a line, determine whether the slope is negative or positive. If the graph is a parabola, determine whether the parabola is concave up (the graph opens up) or concave down (the graph opens down). 3. 4.

Identify the graph of each function as a line or a parabola. If
the graph is a line, determine whether the slope is negative or positive. If the graph is a parabola, determine whether the parabola is concave up (the graph opens up) or concave down (the graph opens down). 5. 6.

Objective 2: Determine the vertex of a parabola.

For a parabola defined by , the x-intercepts
(if they exist) can be determined by using the quadratic formula. The vertex will be located at the x-value midway between the two x-intercepts. See the figure below. y x

7. The x-intercepts of a parabola are and
Determine the x-coordinate of the vertex. 8. The x-intercepts of a parabola are and Determine the x-coordinate of the vertex.

Vertex of the Parabola Defined by
Algebraically Numerically Example: a = −1 and b = 7 The y-values form a symmetric pattern about the vertex. If the table contains the vertex, the y-coordinate of the vertex will be either the largest or the smallest y-value in the table.

Graphically The vertex is either the highest or the lowest point on the parabola. Example:

Finding the Vertex of the Parabola defined
by Step 1. Determine the x-coordinate using Step 2. Then evaluate to determine the y-coordinate.

9. Determine the vertex of the parabola defined by

10. Determine the vertex of the parabola defined by

Use the given equation to calculate the x and y-intercepts and the vertex of each parabola.
11. (a) y-intercept (b) x-intercepts (c) Vertex

Use the given equation to calculate the x and y-intercepts and the vertex of each parabola.
12. (a) y-intercept (b) x-intercepts (c) Vertex

Objective 3: Sketch the graph of a quadratic function
and determine key features of the resulting parabola.

Complete the table, plot the points on the graph, and connect
these points with a smooth parabolic curve. Then complete the missing information. 13. Open upward or downward? Vertex: x-intercepts: y-intercept: Domain: Range: Table Graph

Complete the table, plot the points on the graph, and connect
these points with a smooth parabolic curve. Then complete the missing information. 14. Open upward or downward? Vertex: x-intercepts: y-intercept: Domain: Range: Table Graph

Sketching the Graph of a Quadratic Function
1. Determine whether the parabola opens upward or downward. 2. Determine the coordinates of the vertex. 3. Determine the intercepts. 4. Complete a table using points on both sides of the vertex. 5. Connect all points with a smooth parabolic shape.

15. Sketch the graph of (a) Will the parabola open upward or open downward? (b) Determine the coordinates of the vertex. (c) Complete a table of values using inputs on both sides of the vertex.

15. Sketch the graph of (d) Determine the intercepts of the graph of this function. (e) Use this information to sketch the graph of this function.

16. Sketch the graph of (a) Will the parabola open upward or open downward? (b) Determine the coordinates of the vertex. (c) Complete a table of values using inputs on both sides of the vertex.

16. Sketch the graph of (d) Determine the intercepts of the graph of this function. (e) Use this information to sketch the graph of this function.

Objective 4: Solve problems involving a maximum or
minimum value.

17. gives the profit in dollars when x units are
produced and sold. Use the graph of the profit function to determine the following: Units sold (a) Overhead costs (Hint: Evaluate ) (b) Break even values (Hint: When does ?) (c) Maximum profit that can be made and the number of units to sell to create this profit. Profit in \$

18. A rancher has 240 yards of fencing available to enclose 3
sides of a rectangular corral. A river forms one side of the corral. (a) If x yards are used for the two parallel sides, how much fencing remains for the side parallel to the river? Give this length in terms of x. L = __________________ x L RIVER

18. A rancher has 240 yards of fencing available to enclose 3
sides of a rectangular corral. A river forms one side of the corral. (b) Express the total area of the fenced corral as a function of x. Hint: Area = (Length)(Width) __________________ x L RIVER

18. A rancher has 240 yards of fencing available to enclose 3
sides of a rectangular corral. A river forms one side of the corral. (c) What is the maximum area that can be enclosed with this fencing? Maximum area = __________________ x L RIVER

19. The equation gives the height y of a
baseball in feet x seconds after it was hit. (a) Use the equation to determine how many seconds into the flight the maximum height is reached. (b) Determine the maximum height the ball reached.

19. The equation gives the height y of a
baseball in feet x seconds after it was hit. (c) Do your results agree with what you can observe from the graph? Height (ft) Time (sec)

Use your graphing calculator to determine the minimum/maximum value of
and the x-value at which this minimum/maximum occurs. Use a window of by for each graph. See Calculator Perspective 20. Sketch of calculator graph: Max/min value: x-value where max/min occurs:

Use your graphing calculator to determine the minimum/maximum value of
and the x-value at which this minimum/maximum occurs. Use a window of by for each graph. See Calculator Perspective 21. Sketch of calculator graph: Max/min value: x-value where max/min occurs:

22. Use the function to solve each equation and inequality.
(b) (c)

23. Use the given graph to determine the missing input
and output values. (a) (b)

Use the function to determine the missing input and output values. (a) (b)