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Complex Numbers
Definition of pure imaginary numbers:
Any positive real number b,
where i is the imaginary unit and bi is called the pure
imaginary number.
b2 b2 1 bi
Definition of pure imaginary numbers:
i 1
i2 1
i is not a variable it is a symbol for a specific
number
Simplify each expression.
1. 81 81 1 9i
2. 121x5 121x4 1 x 11x2i x
3. 200x 100 1 2x 10i 2x
4. 8i 3i 24i2 241
Remember i2 1
Simplify each expression.
24
5. 5 20 i 5i 20Remember that 1 i
i2 100 110Remember i
2 1
10
Definition of Complex Numbers
Any number in form a+bi, where a and b are
real numbers and i is imaginary unit.
Definition of Equal Complex Numbers
Two complex numbers are equal if their real parts are equal and their imaginary
parts are equal.If a + bi = c + di,
then a = c and b = d
When adding or subtracting complex numbers, combine like terms.
Ex: 8 3i 2 5i 8 2 3i 5i
10 2i
Solving quadratic functions with complex numbers.
1222 x
-2 -2 subtract 2
102 x Take the square root of both sides
10101 ix simplify
8 7i 1211i
8 12 7i 11i
418i
Simplify.
Simplify.
9 12 6i 2i
3 8i
9 6i 122i
Multiplying complex numbers.
To multiply complex numbers, you use the
same procedure as multiplying polynomials.
Simplify.
8 5i 2 3i
16 24i 10i 15i2F O I L
16 14i 15 31 14i
Simplify.
3018i 10i 6i2F O I L
3028i 6 2428i
62i 5 3i
CONJUGATESEach imaginary unit has a conjugate. Two imaginary units are conjugates if and only if their products are a real number.
i
i
i
2
42
3
i
i
i
2
42
3
4)1)(4(4)2)(2(
2016416884)42)(42(
9)1(99)3)(3(
2
2
2
iii
iiiii
iii
Dividing complex numbers.
To divide complex numbers you must multiply the numerator and denominator by the conjugate of the denominator.
i
i
2
4
What’s the conjugate of the denominator?
5
48
224
48
2
2
2
42
2
i
iii
ii
i
i
i
i
Your turn. Write in standard form by dividing.
i
i
6
32
Graphing complex numbers
y-axis is the imaginary axis. x-axis is the real numbers
Identify the numbers plotted.
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