# High School: Number and Quantity » The Complex Number System

## Standards in this domain:

#### Perform arithmetic operations with complex numbers.

CCSS.Math.Content.HSN.CN.A.1
Know there is a complex number i such that i2 = -1, and every complex number has the form a + bi with a and b real.
CCSS.Math.Content.HSN.CN.A.2
Use the relation i2 = -1 and the commutative, associative, and distributive properties to add, subtract, and multiply complex numbers.
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(+) Find the conjugate of a complex number; use conjugates to find moduli and quotients of complex numbers.

#### Represent complex numbers and their operations on the complex plane.

CCSS.Math.Content.HSN.CN.B.4
(+) Represent complex numbers on the complex plane in rectangular and polar form (including real and imaginary numbers), and explain why the rectangular and polar forms of a given complex number represent the same number.
CCSS.Math.Content.HSN.CN.B.5
(+) Represent addition, subtraction, multiplication, and conjugation of complex numbers geometrically on the complex plane; use properties of this representation for computation. For example, (-1 + √3 i)3 = 8 because (-1 + √3 i) has modulus 2 and argument 120°.
CCSS.Math.Content.HSN.CN.B.6
(+) Calculate the distance between numbers in the complex plane as the modulus of the difference, and the midpoint of a segment as the average of the numbers at its endpoints.

#### Use complex numbers in polynomial identities and equations.

CCSS.Math.Content.HSN.CN.C.7
Solve quadratic equations with real coefficients that have complex solutions.
CCSS.Math.Content.HSN.CN.C.8
(+) Extend polynomial identities to the complex numbers. For example, rewrite x2 + 4 as (x + 2i)(x - 2i).
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(+) Know the Fundamental Theorem of Algebra; show that it is true for quadratic polynomials.