Which statement is true about the imaginary unit $i$?

When solving $x^2=k$ by the square root property, when will the solutions involve $i$?

Why must the symbol $\pm$ be included when solving an equation such as $x^2=25$?

Which expression is equivalent to $\sqrt{-45}$ in simplest form?

Solve $x^2=-50$ and write the solutions in simplest form.