Math Planet
Math Planet: Algebra 2: Complex Numbers
Provides an explanation, examples, and a video lesson all related to complex numbers.
Khan Academy
Khan Academy: Simplify Roots of Negative Numbers
Rewrite square roots of negative numbers as imaginary numbers. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.
Khan Academy
Khan Academy: Powers of the Imaginary Unit
Simplify expressions with base i (the imaginary unit) raised to a positive exponent. Students receive immediate feedback and have the opportunity to try questions repeatedly, watch a video or receive hints.
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.
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.