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 6 Page 108

Make sure the equation is written in standard form. Identify the related function and graph it.

Solutions: No solution.
Graph:

Practice makes perfect

We are asked to solve the given quadratic equation. We will solve it by graphing. To solve a quadratic equation by graphing, we have to follow three steps.

  1. Write the equation in standard form, ax^2+bx+c=0.
  2. Graph the related function f(x)=ax^2+bx+c.
  3. Find the x-intercepts, if any.
The solutions, or roots, of ax^2+bx+c=0 are the x-intercepts of the graph of f(x)=ax^2+bx+c. Let's write our equation in standard form. This means gathering all of the terms on the left-hand side of the equation. - 9 = x^2 ⇔ x^2+9=0

Now we can identify the function related to the equation. Equation:& x^2+9=0 Related Function:& f(x)=x^2+9

Graphing the Related Function

To draw the graph of the related quadratic function written in standard form, we must start by identifying the values of a, b, and c. f(x)=x^2+9 ⇕ f(x)= 1x^2+ 0x+ 9 We can see that a= 1, b= 0, and c= 9. Now, we will follow three steps to graph the function.

  1. Find the axis of symmetry.
  2. Make a table of values using x-values around the axis of symmetry.
  3. Plot and 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=- 0/2( 1)
â–Ľ
Evaluate right-hand side
x=-0/2
x=0
The axis of symmetry of the parabola is the vertical line with equation x=0.

Making the Table of Values

Next, we will make a table of values using x-values around the axis of symmetry x=0.

x x^2+9 f(x)
- 3 ( - 3)^2+9 18
- 1.5 ( - 1.5)^2+9 11.25
0 0^2+9 9
1.5 1.5^2+9 11.25
3 3^2+9 18

Plotting and Connecting the Points

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

We can see that the parabola does not intersect the x-axis. Therefore, it has no real solutions.