Make x the subject of the formula y equals xsquared plus 2mx plus n?

y = x2 + 2mx + n

complete the square

y + m2 = x2 + 2mx + m2 + n = (x + m)2 + n

(x + m)2 = y + m2 - n

x + m = √(y + m2 - n)

x = -m + √(y + m2 - n)