Unit 2 – Quadratic, Polynomial, and Radical Equations and Inequalities Chapter 5 – Quadratic Functions and Inequalities 5.4 – Complex Numbers

5.4 – Complex Numbers In this section we will learn how to: Find square roots and perform operations with pure imaginary numbers Perform operations with complex numbers

5.4 – Complex Numbers Square root – the square root of a number n is a number with a square of n. Ex. 7 is a square root of 49 because 72 = 49 Since (-7)2 = 49, -7 is also a square root

5.4 – Complex Numbers Product and Quotient Properties of Square Roots For nonnegative real numbers a and b, √ab = √a  √b Ex. √3  2 = √3  √2 √a/b = √a / √b Ex. √1/4 = √1 / √4

5.4 – Complex Numbers Simplified square root expressions DO NOT have radicals in the denominator. Any number remaining under the square root has no perfect square factor other than 1.

5.4 – Complex Numbers Example 1 Simplify √18 √10/81

5.4 – Complex Numbers Example 2 Simplify √-9 IMAGINARY NUMBER!!

5.4 – Complex Numbers Imaginary number – created so that square roots of negative numbers can be found Imaginary unit – i i = √-1 i2 = –1 i3 = – I i4 = 1 Pure imaginary number – square roots of negative real numbers Ex. 3i, -5i, and i√2 For any positive real number b, √-b2 = √b2  √-1 or bi

5.4 – Complex Numbers Example 3 Simplify √-28 √-32y4

5.4 – Complex Numbers Example 4 Simplify -3i  2i √-12  √-2 i35

5.4 – Complex Numbers You can solve some quadratic equations by using the square root property Square Root Property For any real number n, if x2 = n, then x = ±√n

5.4 – Complex Numbers Example 5 Solve 5y2 + 20 = 0.

5.4 – Complex Numbers HOMEWORK Page 264 #22 – 29

5.4 – Complex Numbers Complex number – any number that can be written in the form a + bi, where a and b are real numbers and i is the imaginary unit. a is called the real part, and b is called the imaginary part Ex. 5 + 2i and 2 – 6i = 2 + (-6)I If b = 0, the complex number is a real number If b ≠ 0, the complex number is imaginary If a = 0, the complex number is a pure imaginary number

5.4 – Complex Numbers Two complex numbers are equal if and only if (IFF) their real parts are equal AND their imaginary parts are equal. a + bi = c + di IFF a = c and b = d

5.4 – Complex Numbers Example 6 Find the values of x and y that make that equation 2x + yi = -14 – 3i true.

5.4 – Complex Numbers To add or subtract complex numbers, combine like terms. Combine the real parts Combine the imaginary parts

5.4 – Complex Numbers Example 7 Simplify (3 + 5i) + (2 – 4i)

5.4 – Complex Numbers You can also multiply 2 complex numbers using the FOIL method

5.4 – Complex Numbers Example 8 In an AC circuit, the voltage E, current I, and impedance Z are related by the formula E = I  Z. Find the voltage in a circuit with current 1 + 3j amps and impedance 7 – 5j ohms.

5.4 – Complex Numbers HOMEWORK Page 264 #30 – 39

5.4 – Complex Numbers Complex conjugates – two complex numbers of the form a + bi and a – bi. The product of complex conjugates is always a real number. You can use this to simplify the quotient of two complex numbers.

5.4 – Complex Numbers Example 9 Simplify

5.4 – Complex Numbers HOMEWORK Page 264 #40 – 49