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k in (-oo:+oo)
k^2 = 49/64 // - 49/64
k^2-(49/64) = 0
k^2-49/64 = 0
1*k^2 = 49/64 // : 1
k^2 = 49/64
k^2 = 49/64 // ^ 1/2
abs(k) = 7/8
k = 7/8 or k = -7/8
k in { 7/8, -7/8 }
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