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You can calculate odd root of negative numbers. Examples. 3th root of -8 equal -2 because (-2)^3 = -8. 5th root of -32 equal -2 because (-2)^5 = -32. 5th root of -243 equal -3 because (-3)^5 = -32. 3th root of -8/27 equal -2/3 because (-2/3)^3 equal -8/27. Calculate even root of negative numbers is not possible because odd power negative or positive number never give number under root, e.g. 4th root of -16 not equal -2 because (-2)^4 not equal -16.