Solve the Equation by the Square Root Property $$x ^ { 2 } = - 81$$

Multiple Choice

Solve the equation by the square root property.
- $$x ^ { 2 } = - 81$$

A) $\{ \pm 9 \}$
B) $\{ 40.5 \}$
C) $\{ \pm 9 i \}$
D) $\{ 9 \}$