A complex number is a number of the form a + bi, where a, b are real "coefficients" called the real and imaginary part. Just like n often represents an integer, z often represents a complex number. All real numbers (like 0.5, √3, π, ...) are complex numbers, as are all imaginary numbers (like 0.5i, i√3, πi, ...). Additionally, this covers basic addition and subtraction of complex numbers as an extension of combining like terms.