Answer:
12b. 28 = x
12a. -7 = x
11b. -6 = x
11a. 9 = x
10b. UNDEFINED
10a. -⅕ = x
9b. i = x
9a. ±3 = x
Explanation:
12. Cube both sides of both equations, then solve for x:
![12b. \: 3 = \sqrt[3]{x - 1} >> 27 = x - 1 \\ \\ 28 = x \\ \\ 12a. \: -2 = \sqrt[3]{x - 1} >> -8 = x - 1 \\ \\ -7 = x](https://img.qammunity.org/2020/formulas/mathematics/high-school/zyuq3s7q0acyt00jbk02mi3mk6b8bcmgzp.png)
11. Square both sides of both equations, then solve for x:

10. Dividing is the same as multiplying by the multiplicative inverse of another term:

* ⁻¹ indicates the multiplicative inverse of -⅕, which is -5. Then there is 1⁄0, which is undefined.
9.

+ 5 + 5
____________________
-1 = x²

According to the Complex Number System, the iota symbol can be either complex or real:

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