The result ‘sqrt(x)^2’ is simplified back to ‘x’ by the Calculator, but ‘sqrt(x^2)’ is not. (Consider what happens if ‘x = -4’.) If ‘x’ is real, this formula could be simplified to ‘abs(x)’, but for general complex arguments even that is not safe. (See Declarations, for a way to tell Calc that ‘x’ is known to be real.)