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**Unit 2 – Quadratic, Polynomial, and Radical Equations and Inequalities**

Chapter 5 – Quadratic Functions and Inequalities 5.6 – The Quadratic Formula and the Discriminant

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**5.6 – The Quadratic Formula and the Discriminant**

In this section we will learn how to: Solve quadratic equations by using the Quadratic Formula Use the discriminant to determine the number and type of roots of a quadratic equation.

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**5.6 – The Quadratic Formula and the Discriminant**

Exact solutions to some quadratic equations can be found by graphing, factoring or by using the Square Root Property. Completing the square can be used to solve any quadratic equation, but it can be tedious if the equations have fractions/decimals Fortunately, a formula exists that can be used to solve any quadratic equation of the form ax2 + bx + c = 0

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**5.6 – The Quadratic Formula and the Discriminant**

ax2 + bx + c = 0

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**5.6 – The Quadratic Formula and the Discriminant**

The solutions of a quadratic equation of the form ax2 + bx + c = 0, where a ≠ 0, are given by the following formula: x= -b ± √b2-4ac 2a

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**5.6 – The Quadratic Formula and the Discriminant**

Example 1 Solve x2 – 8x = 33 by using the Quadratic Formula

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**5.6 – The Quadratic Formula and the Discriminant**

Example 2 Solve x2 – 34x +289 = 0 by using the Quadratic Formula When the value of the radicand is 0, there is only one rational root

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**5.6 – The Quadratic Formula and the Discriminant**

Example 3 Solve x2 – 6x + 2 = 0 by using the Quadratic Formula.

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**5.6 – The Quadratic Formula and the Discriminant**

Example 4 Solve x = 6x by using the Quadratic Formula

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**5.6 – The Quadratic Formula and the Discriminant**

The expression b2 – 4ac is called the discriminant The value of the discriminant can be used to determine the number and type of roots of a quadratic equation.

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**5.6 – The Quadratic Formula and the Discriminant**

Consider ax2 + bx + c = 0, where a, b, and c are rational numbers Value of Discriminant Type and number of roots Example of Graph of Related Function b2 – 4ac > 0; b2 – 4ac is a perfect square 2 real, rational roots b2 – 4ac is not a perfect square 2 real, irrational roots b2 – 4ac = 0 1 real, rational root b2 – 4ac < 0 2 complex roots

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**5.6 – The Quadratic Formula and the Discriminant**

The discriminant can help you check the solutions of a quadratic equation. Your solutions must match in number and in type to those determined by the discriminant

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**5.6 – The Quadratic Formula and the Discriminant**

Example 5 Find the value of the discriminant for each quadratic equation. Describe the number and type of roots for the equation. x2 + 3x + 5 = 0 x2 – 11x + 10 = 0

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**5.6 – The Quadratic Formula and the Discriminant**

Method Can be Used When to Use Example Graphing sometimes Use only if an exact answer is not required Factoring Use if the constant term is 0 or if the factors are easily determined x2 – 3x = 0 Square Root Property Use for equations in which a perfect square is equal to a constant (x + 13)2 = 9 Completing the Square always Useful for equations of the form x2 + bx + c = 0 when b is even x2 + 14x – 9 = 0 Quadratic Formula Useful when other methods fail or are too tedious 3.4x2 – 2.5x = 0

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**5.6 – The Quadratic Formula and the Discriminant**

HOMEWORK Page 281 #15 – 45 odd

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