Subjects

Algebra 2

Complex Numbers & Unit I

The Imaginary Unit I

•

Dec 7, 2025

•

3 pages

Understanding Imaginary Numbers: Simple Definitions and Solving Techniques

Asiya

@ciya

Complex numbers combine real and imaginary parts, allowing us to... Show more

1 / 3

$Quadratic Formula *write real #'s first* $x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}$ $a + bi$ real # imaginary # $i = \sqrt{-1}$ $i^2 = -1$ S$

Complex Numbers and the Imaginary Unit

Ever wondered how to take the square root of a negative number? That's where complex numbers come in! A complex number has the form a + bi, where a is the real part and bi is the imaginary part.

The imaginary unit i is defined as √(-1), which means i² = -1. This lets us work with square roots of negative numbers by writing them in terms of i. For example, √(-25) = √(-1 · 25) = √(-1) · √25 = 5i.

The powers of i follow a cycle of four: i¹ = i, i² = -1, i³ = -i, and i⁴ = 1. This pattern repeats, making it easy to find higher powers like i²⁰²⁴ = 1 (since 2024 is divisible by 4).

Quick Tip: When adding or subtracting complex numbers, simply combine the real parts and combine the imaginary parts separately: $a+bi$ + $c+di$ = $a+c$ + $b+d$ i

$Quadratic Formula *write real #'s first* $x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}$ $a + bi$ real # imaginary # $i = \sqrt{-1}$ $i^2 = -1$ S$

Operations with Complex Numbers

Simplifying square roots of negative numbers becomes second nature with practice. For example, √(-32) = √(-1 · 32) = i · √32 = i · 4√2 = 4i√2.

When multiplying two complex numbers, use the FOIL method just like with binomials. For instance, $3-4i$ $6+i$ = 18+3i-24i-4i² = 22-21i $remember that i² = -1$ .

Adding and subtracting complex numbers is straightforward - just combine like terms. For $5+2i$ + $4-3i$ , add the real parts (5+4) and add the imaginary parts $2i-3i$ to get 9-i.

Multiplication Shortcut: When multiplying a complex number by its conjugate $a+bi$ $a-bi$ , you always get a real number: a²+b². This is super helpful for division problems!

$Quadratic Formula *write real #'s first* $x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}$ $a + bi$ real # imaginary # $i = \sqrt{-1}$ $i^2 = -1$ S$

Complex Conjugates and Division

The complex conjugate of a+bi is a-bi. Conjugates are incredibly useful when dividing complex numbers because their product is always a real number $a²+b²$ .

To divide complex numbers, multiply both the numerator and denominator by the conjugate of the denominator. This eliminates the imaginary part in the denominator, giving you a standard complex number form.

For example, to calculate $3+i$ / $2-3i$ , multiply by the conjugate $2+3i$ / $2+3i$ . This gives you $3+i$ $2+3i$ / $2-3i$ $2+3i$ = $3+11i$ /13.

Remember: When dividing complex numbers, your final answer should always be in the standard form a+bi with no imaginary numbers in the denominator.

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Subjects

Algebra 2

Complex Numbers & Unit I

The Imaginary Unit I

Algebra 2

•

Dec 7, 2025

•

3 pages

Understanding Imaginary Numbers: Simple Definitions and Solving Techniques

Asiya

@ciya

Complex numbers combine real and imaginary parts, allowing us to work with square roots of negative numbers. They're essential for solving quadratic equations that have no real solutions and form the foundation for advanced math and physics concepts.

$Quadratic Formula *write real #'s first* $x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}$ $a + bi$ real # imaginary # $i = \sqrt{-1}$ $i^2 = -1$ S$

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Complex Numbers and the Imaginary Unit

Ever wondered how to take the square root of a negative number? That's where complex numbers come in! A complex number has the form a + bi, where a is the real part and bi is the imaginary part.

The powers of i follow a cycle of four: i¹ = i, i² = -1, i³ = -i, and i⁴ = 1. This pattern repeats, making it easy to find higher powers like i²⁰²⁴ = 1 (since 2024 is divisible by 4).

Quick Tip: When adding or subtracting complex numbers, simply combine the real parts and combine the imaginary parts separately: $a+bi$ + $c+di$ = $a+c$ + $b+d$ i

$Quadratic Formula *write real #'s first* $x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}$ $a + bi$ real # imaginary # $i = \sqrt{-1}$ $i^2 = -1$ S$

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Operations with Complex Numbers

Simplifying square roots of negative numbers becomes second nature with practice. For example, √(-32) = √(-1 · 32) = i · √32 = i · 4√2 = 4i√2.

When multiplying two complex numbers, use the FOIL method just like with binomials. For instance, $3-4i$ $6+i$ = 18+3i-24i-4i² = 22-21i $remember that i² = -1$ .

Adding and subtracting complex numbers is straightforward - just combine like terms. For $5+2i$ + $4-3i$ , add the real parts (5+4) and add the imaginary parts $2i-3i$ to get 9-i.

Multiplication Shortcut: When multiplying a complex number by its conjugate $a+bi$ $a-bi$ , you always get a real number: a²+b². This is super helpful for division problems!

$Quadratic Formula *write real #'s first* $x = \frac{-b \pm \sqrt{b^2-4ac}}{2a}$ $a + bi$ real # imaginary # $i = \sqrt{-1}$ $i^2 = -1$ S$

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Complex Conjugates and Division

The complex conjugate of a+bi is a-bi. Conjugates are incredibly useful when dividing complex numbers because their product is always a real number $a²+b²$ .

For example, to calculate $3+i$ / $2-3i$ , multiply by the conjugate $2+3i$ / $2+3i$ . This gives you $3+i$ $2+3i$ / $2-3i$ $2+3i$ = $3+11i$ /13.

Remember: When dividing complex numbers, your final answer should always be in the standard form a+bi with no imaginary numbers in the denominator.