The square root of a fraction is sometimes easier to evaluate by taking the square root of the numerator and denominator separately. $$\sqrt{\frac{9}{4}}=\frac{\sqrt{9}}{\sqrt{4}}=\frac{3}{2}$$ This rule yields for all real numbers where the denominator is not $0.$ However, in order to avoid non-real solutions it is necessary that the numerator and the denominator are non-negative numbers.