# 7.4 Solving Polynomial Equations

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7.4 Solving Polynomial Equations
Objectives: Solve polynomial equations Find the real zeros of polynomial functions and state the multiplicity of each

Example 1 Use factoring to solve 5x3 – 12x2 + 4x = 0.

Example 2 Use a graph, synthetic division, and factoring to find all roots of x3 + 3x2 – 4 = 0. First, graph the polynomial function to approximate the roots. Then use synthetic division to test your choices. 1 1 4 4 1 4 4 Since the remainder is 0, x – 1 is a factor of x3 + 3x2 - 4.

Example 2 Use a graph, synthetic division, and factoring to find all roots of x3 + 3x2 – 4 = 0. Since the remainder is 0, x – 1 is a factor of x3 + 3x2 - 4. x3 + 3x2 – 4 = 0 (x – 1)(x2 + 4x + 4) = 0 (x – 1)(x + 2)(x + 2) = 0 x = 1 x = -2 x = -2 The roots of x3 + 3x2 – 4 are 1 and -2, with the root -2 occurring twice.

Practice Use a graph, synthetic division, and factoring to find all of the roots of x3 + 2x2 – 4x – 8 = 0.

Example 3 Use variable substitution and factoring to find all roots of x4 – 5x2 – 6 = 0. Substitute u for x2 in the above equation and then solve for u. (x2)2 – 5(x2) – 6 = 0 u2 – 5u – 6 = 0 (u – 6)(u + 1) = 0 u = 6 u = -1 x2 = 6 x2 = -1

Practice Use variable substitution and factoring to find all of the roots of x4 – 9x = 0.

Example 4 Find the real zeros of the function. Give approximate values to the nearest hundredth, if necessary. f(x) = x4 – 10x3 + 22x2 + 20x - 48 x = 4 x = 6 x = 1.41 x = -1.41

Homework Lesson 7.4 Exercises odd and odd