Hmm, "undefined" is wrong, too, but maybe better than the wrong numeric result 1.
BTW, muPad in MC15 returns "undefined" for the first expression as well, but is not able to evaluate the other two (it returns "undefined" here, too). It needs a little manual help by slightly reshaping the expression:
So we have one of the rare examples where the new symbolic performs better 😉
Wolfram times out on the first expression
but the CAS in the free GeoGebra does a pretty good job on this
GeoGebra seems to achieve this result by rewriting the absolute value function and also the alternate sign of (-7)^k in a creative way. It seems to automatically assume k being an integer as otherwise (-7)^k would not be defined in the set of real numbers.
Not sure if I should like that automatic behaviour...
