Trigonometry (11th Edition) Clone

{$\pm 9i$}
Step 1: $x^{2}=-81$ Step 2: Using the square root property, $x=\pm\sqrt {-81}$ Step 3: $x=\pm\sqrt {-1\times81}$ Step 4: Using the product rule for radicals, $x=\pm\sqrt {-1}\times\sqrt {81}$ Step 5: Since $i=\sqrt {-1}$, $x=\pm i\times\sqrt {81}$ Step 6: $x=\pm i\times9$ Step 7: $x=\pm 9i$ Therefore, the solution set is {$\pm 9i$}.