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b in (-oo:+oo)
2/7-((1/4)*b) = 1/28 // - 1/28
2/7-((1/4)*b)-(1/28) = 0
(-1/4)*b+2/7-1/28 = 0
1/4-1/4*b = 0 // - 1/4
-1/4*b = -1/4 // : -1/4
b = -1/4/(-1/4)
b = 1
b = 1
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