We have to compute this .. on a computer

seems very easy, but me and my partner cant agree on something

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I say that this is to be see as

X = b^{m/n }

b being negative and n being even, the answer is the complex number5i

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my partner says:

this should be see as

X = (b^{m})^{1/n}

giving the answer 5 and -5

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I say that he is wrong because:

if I reverse the function,

((-5)^{4})^{1/2 }= 25, not -25

((-5)^{1/2)}^{4 }= 25, not -25

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and

((5i)^{1/2)}^{4 }= -25

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but he wont see this as a proof since the programs "Maple" and also "Microsoft Math" does return 5 and -5

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Please, tell me who is right ??