# SWBAT… use the Quadratic Formula to solve quadratic equations Fri, 5/10 Agenda 1. WU (15 min) 2. Quadratic Formula (30 min) Warm-Up: Given y = x 2 + 5x.

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SWBAT… use the Quadratic Formula to solve quadratic equations Fri, 5/10 Agenda 1. WU (15 min) 2. Quadratic Formula (30 min) Warm-Up: Given y = x 2 + 5x + 6 1. Find the domain and range 2. Find the solutions HW#5: Study Guide

The Quadratic Formula YOU MUST MEMORIZE THIS FORMULA!!!

What Does The Formula Do? The Quadratic formula allows you to find the roots of a quadratic equation (if they exist) even if the quadratic equation does not factorise. The formula states that for a quadratic equation of the form : ax 2 + bx + c = 0 The roots of the quadratic equation are given by :

Example 1 Use the quadratic formula to solve the equation x 2 + 5x + 6 = 0 Solution: x 2 + 5x + 6 = 0 a = 1 b = 5 c = 6 x = -2 or x = -3 These are the roots of the equation.

Example 2 Use the quadratic formula to solve the equation 8x 2 + 2x – 3= 0 Solution: 8x 2 + 2x – 3 = 0 a = 8 b = 2 c = -3 x = ½ or x = -¾ These are the roots of the equation.

Example 3 Use the quadratic formula to solve the equation 8x 2 – 22x + 15 = 0 Solution: 8x 2 – 22x + 15 = 0 a = 8 b = -22 c = 15 x = 3/2 or x = 5/4 These are the roots of the equation.

a = -2 b = 5 c = 3 x = ½ or x = -3/4 What is wrong with this student’s work? What are the correct solutions? Use the quadratic formula to solve the equation -2x 2 + 5x + 3= 0

a = -2 b = 5 c = 3 x = -2/4 = -1/2 or x = 3 Use the quadratic formula to solve the equation -2x 2 + 5x + 3= 0 Example 4

The Discriminant In the Quadratic Formula, the expression under the radical sign, b 2 – 4ac is called the discriminant. The discriminat can be used to determine the number of real solutions of a quadratic equation.

Key Concept: Using the Discriminant Equation Example Discriminant Graph of Related Function Number of Real Solutions

Key Concept: Using the Discriminant Equation Example x 2 + 2x + 5 = 0x 2 + 10x + 25 = 02x 2 – 7x + 2 = 0 Discriminant Graph of Related Function Number of Real Solutions

Key Concept: Using the Discriminant Equation Example x 2 + 2x + 5 = 0x 2 + 10x + 25 = 02x 2 – 7x + 2 = 0 DiscriminantNegativeZeroPositive Graph of Related Function Number of Real Solutions

Key Concept: Using the Discriminant Equation Example x 2 + 2x + 5 = 0x 2 + 10x + 25 = 02x 2 – 7x + 2 = 0 DiscriminantNegativeZeroPositive Graph of Related Function 0 x-intercepts1 x-intercepts2 x-intercepts Number of Real Solutions

Key Concept: Using the Discriminant Equation Example x 2 + 2x + 5 = 0x 2 + 10x + 25 = 02x 2 – 7x + 2 = 0 DiscriminantNegativeZeroPositive Graph of Related Function 0 x-intercepts1 x-intercepts2 x-intercepts Number of Real Solutions 012

SWBAT… use the Quadratic Formula to solve quadratic eqns. Tues, 5/24 Agenda 1. WU (10 min) 2. Review HW#5 (10 min) 3. HW#6 – Study Guide WARM-UP Given the function f(x) = 3x 2 – 18x + 15, for what values of x does f(x) = 0. HW#6: Quadratics Study Guide

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