${p}^{2}=100$
Take the square root of both sides of the equation and remember to use both positive and negative roots$p=10$
Write the solutions, one with a $+$ sign and one with a $-$ sign$\begin{array} { l }p=-10,\\p=10\end{array}$
The equation has $2$ solutions$\begin{array} { l }p_1=-10,& p_2=10\end{array}$