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m in (-oo:+oo)
(-4/5)*m+(1/7)*m+4 = 257/70 // - 257/70
(-4/5)*m+(1/7)*m-(257/70)+4 = 0
(-4/5)*m+(1/7)*m-257/70+4 = 0
23/70-23/35*m = 0 // - 23/70
-23/35*m = -23/70 // : -23/35
m = -23/70/(-23/35)
m = 1/2
m = 1/2
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