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GNU Emacs Calc 2.02 Manual

3.7.48 Algebra Tutorial Exercise 1

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 section 7.6 Declarations, for a way to tell Calc that x is known to be real.)