1. Solving Quadratic Equations by the Quadratic Formula
Adapted by Christopher Carnes, Rancho Viejo MS, Hemet, CA
Tuesday, March 15, 2016

2. How can we use the Quadratic Formula to solve quadratic equations?
Essential Question:
How can we use the Quadratic Formula to solve quadratic equations?

3. THE QUADRATIC FORMULA
When you solve using completing the square on the general formula you get:
This is the quadratic formula!
Just identify a, b, and c then substitute into the formula.

4. WHY USE THE QUADRATIC FORMULA?
The quadratic formula allows you to solve ANY quadratic equation, even if you cannot factor it.
An important piece of the quadratic formula is what’s under the radical:
b2 – 4ac
This piece is called the discriminant.

5. WHY IS THE DISCRIMINANT IMPORTANT?
The discriminant tells you the number and types of answers
(roots) you will get. The discriminant can be +, –, or 0
which actually tells you a lot! Since the discriminant is
under a radical, think about what it means if you have a
positive or negative number or 0 under the radical.

6. WHAT THE DISCRIMINANT TELLS YOU!
Value of the Discriminant
Nature of the Solutions
Negative
2 imaginary solutions
Zero
1 Real Solution
Positive – perfect square
2 Reals- Rational
Positive – non-perfect square
2 Reals- Irrational

7. Example #1 a=2, b=7, c=-11 Discriminant = Discriminant =
Find the value of the discriminant and describe the nature of the roots (real,imaginary, rational, irrational) of each quadratic equation. Then solve the equation using the quadratic formula) 1.
a=2, b=7, c=-11
Discriminant =
Value of discriminant=137
Positive-NON perfect square
Nature of the Roots – 2 Reals - Irrational
Discriminant =

8. Example #1- continued
Solve using the Quadratic Formula

9. Solving Quadratic Equations by the Quadratic Formula
Try the following examples. Do your work on your paper and then check your answers.