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k in (-oo:+oo)
(2/5)/12 = k+(-3/1)/4 // - k+(-3/1)/4
(2/5)/12-k-((-3/1)/4) = 0
(2/5)/12-k+3/4 = 0
47/60-k = 0 // - 47/60
-k = -47/60 // * -1
k = 47/60
k = 47/60
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