CK-12 Foundation
Ck 12: 1.5 From Quadratics to Complex Numbers
This section introduces imaginary and complex numbers in the context of solutions to quadratic equations that don't have real-number solutions.
Math Planet
Math Planet: Algebra 2: Complex Numbers
Provides an explanation, examples, and a video lesson all related to complex numbers.
CK-12 Foundation
Ck 12: Algebra Ii: 1.6 the Complex Plane
This section includes operations with imaginary and complex numbers and plotting numbers on the complex plane.
Mathigon
Mathigon: Real, Irrational, Imaginary Numbers
Explore this course in imaginary and complex numbers including topics of integers, real numbers, infinity, transcendental numbers, imaginary and complex numbers.