Subtract $16$ from both sides. Anything subtracted from zero gives its negation.
$$x^{2}=-16$$
The equation is now solved.
$$x=4i$$ $$x=-4i$$
Steps Using the Quadratic Formula
Quadratic equations like this one, with an $x^{2}$ term but no $x$ term, can still be solved using the quadratic formula, $\frac{-b±\sqrt{b^{2}-4ac}}{2a}$, once they are put in standard form: $ax^{2}+bx+c=0$.
$$x^{2}+16=0$$
This equation is in standard form: $ax^{2}+bx+c=0$. Substitute $1$ for $a$, $0$ for $b$, and $16$ for $c$ in the quadratic formula, $\frac{-b±\sqrt{b^{2}-4ac}}{2a}$.
$$x=\frac{0±\sqrt{0^{2}-4\times 16}}{2}$$
Square $0$.
$$x=\frac{0±\sqrt{-4\times 16}}{2}$$
Multiply $-4$ times $16$.
$$x=\frac{0±\sqrt{-64}}{2}$$
Take the square root of $-64$.
$$x=\frac{0±8i}{2}$$
Now solve the equation $x=\frac{0±8i}{2}$ when $±$ is plus.
$$x=4i$$
Now solve the equation $x=\frac{0±8i}{2}$ when $±$ is minus.
