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# Unit 5: Complex numbers

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## About this unit

Complex numbers are built on the idea that we can define the number i (called "the imaginary unit") to be the principal square root of -1, or a solution to the equation x²=-1. From this starting point evolves a rich and exciting world of the number system that encapsulates everything we have known before: integers, rational, and real numbers.### Learn

### Practice

- Simplify roots of negative numbersGet 3 of 4 questions to level up!
- Powers of the imaginary unitGet 3 of 4 questions to level up!

### Learn

### Practice

- Parts of complex numbersGet 3 of 4 questions to level up!
- Classify complex numbersGet 3 of 4 questions to level up!

### Practice

- Plot numbers on the complex planeGet 3 of 4 questions to level up!

Level up on the above skills and collect up to 400 Mastery points

### Practice

- Add & subtract complex numbersGet 3 of 4 questions to level up!

### Learn

### Practice

- Multiply complex numbers (basic)Get 3 of 4 questions to level up!
- Multiply complex numbersGet 3 of 4 questions to level up!

### Practice

- Solve quadratic equations: complex solutionsGet 3 of 4 questions to level up!

Level up on the above skills and collect up to 320 Mastery points

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Level up on all the skills in this unit and collect up to 900 Mastery points!