Hello, I am having trouble with the following problem:

If the vector

I have the answer key which says 1/2^1/2 and -1/2^1/2 are the possible values of a. It also says that the norm of

If the vector

**u**= (1/2, a, 0, -1/2) is a unit Vector, find possible values of a.I have the answer key which says 1/2^1/2 and -1/2^1/2 are the possible values of a. It also says that the norm of

**u**is 1. The part I am having trouble with is finding out the norm of**u**. Once I know the norm I can find a. What am I missing here? Thanks.
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