An algebra problem by Brian Wang

${ x }^{ 2 }\quad =\quad 25\\ x\quad =\quad \pm \sqrt { 25 } \\ x\quad =\quad \boxed { \pm 5 }$

My teacher repeatedly point this out. \sqrt{x} only have positive result for x as the value for x in the square root can only take positive value. If it asks x = \sqrt{y}, then x can be both negative and positive