If [[$ \sqrt{a} = b$]], then [[$ b^2 =a $]] and [[$ b\geq 0$]] (applies both ways).

Calculation rules

[[$ (\sqrt{a})^2 = a$]]

[[$ \sqrt{a^2} = |a|$]]

[[$ \sqrt{\dfrac{a}{b}} = \dfrac{\sqrt{a}}{\sqrt{b}}$]]

[[$ \sqrt{ab} = \sqrt{a}\sqrt{b}$]]