McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
2. Solving Quadratic Equations by Graphing
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Exercise 10 Page 108

Start by identifying the values of a, b, and c.

Graph:

Solutions: No real solutions

Practice makes perfect
We want to solve the given quadratic equation by graphing. x^2+7x+14=0 To do so, we will graph the quadratic function represented by the left-hand side of the above equation. To draw the graph, we must start by identifying the values of a, b, and c. y=x^2+7x+14 ⇔ y= 1x^2+ 7x+ 14

We can see that a= 1, b= 7, and c= 14. Now, we will follow four steps to graph the function.

  1. Find the axis of symmetry.
  2. Calculate the vertex.
  3. Identify the y-intercept and its reflection across the axis of symmetry.
  4. Connect the points with a parabola.

Finding the Axis of Symmetry

The axis of symmetry is a vertical line with equation x=- b2 a. Since we already know the values of a and b, we can substitute them into the formula.
x=- b/2a
x=- 7/2( 1)
x=- 7/2
x=-3.5
The axis of symmetry of the parabola is the vertical line with equation x=-3.5.

Calculating the Vertex

To calculate the vertex, we need to think of y as a function of x, y=f(x). We can write the expression for the vertex by stating the x- and y-coordinates in terms of a and b. Vertex: ( - b/2 a, f( - b/2 a ) ) Note that the formula for the x-coordinate is the same as the formula for the axis of symmetry, which is x=-3.5. Thus, the x-coordinate of the vertex is also -3.5. To find the y-coordinate, we need to substitute -3.5 for x in our function.
y=x^2+7x+14
y=( -3.5)^2+7( -3.5)+14
â–Ľ
Simplify right-hand side
y=12.25+7(-3.5)+14
y=12.25-24.5+14
y=1.75
We found the y-coordinate, and now we know that the vertex is (-3.5,1.75).

Identifying the y-intercept and its Reflection

The y-intercept of the graph of a quadratic function written in standard form is given by the value of c. Thus, the point where our graph intercepts the y-axis is (0, 14). Let's plot this point and its reflection across the axis of symmetry.

Connecting the Points

We can now draw the graph of the function. Since a= 1, which is positive, the parabola will open upward. Let's connect the three points with a smooth curve.

The x-intercepts of the graph are the solutions to the given equation. However, this graph has no x-intercepts. Therefore, this equation has no real solutions.