Multiplying Complex Numbers Adapted from Walch Education
Key Concepts Simplify any powers of i before evaluating products of complex numbers. Find the product of the first terms, outside terms, inside terms, and last terms. Note: The imaginary unit i follows the product of real numbers : Multiplying Complex Numbers 2
Key Concepts, continued A complex conjugate is a complex number that when multiplied by another complex number produces a value that is wholly real. The complex conjugate of a + bi is a – bi, and the complex conjugate of a – bi is a + bi. The product of a complex number and its conjugate is the difference of squares, a 2 – (bi) 2, which can be simplified. a 2 – b 2 i 2 = a 2 – b 2 (–1) = a 2 + b : Multiplying Complex Numbers 3
Practice Find the result of i 2 5i : Multiplying Complex Numbers 4
The Solution Simplify any powers of i. Multiply the two terms. Simplify the expression, if possible, by simplifying any remaining powers of i or combining like terms. 5(–i) = –5i 4.3.3: Multiplying Complex Numbers 5
Can you Find the result of (7 + 2i)(4 + 3i) : Multiplying Complex Numbers 6
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