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n in (-oo:+oo)
(2/7)*n-3 = -89/28 // + -89/28
(2/7)*n-(-89/28)-3 = 0
(2/7)*n+89/28-3 = 0
2/7*n+5/28 = 0 // - 5/28
2/7*n = -5/28 // : 2/7
n = -5/28/2/7
n = -5/8
n = -5/8
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