question_answer

For which value of k does the pair of equations \[{{x}^{2}}-{{y}^{2}}=0\] and \[{{(x-k)}^{2}}+{{y}^{2}}=1\] yield a unique positive solution for x?

A)  2                                

B)  0

C)  \[\sqrt{2}\]                   

D)  \[-\,\sqrt{2}\]

E)  None of these