Verified answer

x = 2^k

sqr (4/x) = 2^c

sqr (4 / (2^k)) = 2^c

sqr (2^2 / 2^k) = 2^c

(2^2 / 2^k)^(1/2) = 2^c

(2^(2 - k))^(1/2) = 2^c

2^((1/2) (2 - k)) = 2^c

2^(1 - k/2) = 2^c

<=>

c = 1 - k/2 = (2 - k) / 2

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erm wow