• Definition of complex numbers: Complex numbers are of the form a + bi, where i is the square root of -1.
• Algebraic form: A complex number z is in the form z = a + bi, where a and b are real numbers.
• Conjugate and properties: The conjugate of a complex number changes the sign of its imaginary part; the real part of z is a, and the imaginary part is b.
• Equivalent forms: Complex numbers can also be expressed in exponential form, z = |z|(cos θ + i sin θ), where |z| is the module of the complex number and θ is its argument.
• Equation solving: To solve a quadratic complex equation az² + bz + c = 0, the quadratic formula is used: z = (-b ± √(b² - 4ac)) / (2a).

For a deeper understanding and improvement of skills in solving complex equations, high school students can find PDF courses and exercises on complex numbers online. These resources include solved exercises, course summaries, and practical examples.