If in the last solution, you meant to have all of the expression 2(s-v)/a under the square root, then parantheses should have been included for the sake of readability: It should have been sqrt(2(s-v)/a).

If parantheses are not included, then it becomes unclear exactly what part of the expression belongs under the square root. For instance, I could also read "sqrt 2(s-v)/a" as

sqrt(2)*(s-v)/a,

or

sqrt(2(s-v))/a,

these being entirely different expressions.