Chapter 4 Quadratic Functions and Factoring - 4.6 Perform Operations with Complex Numbers - 4.6 Exercises - Skill Practice - Page 279: 5

$$\ z=\pm 2i$$

For imaginary numbers, we know that standard form is $a\pm bi$, where $a$ is the real part and $b$ is the imaginary part. To get the expression into this form, we combine like terms like we did with polynomials. Doing this, we find: $$z^2=-4 \\ z=\pm 2i$$