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x in (-oo:+oo)
10 = (3.99-x)/3.99 // - (3.99-x)/3.99
10-((3.99-x)/3.99) = 0
10-0.25062657*(3.99-x) = 0
10-0.25062657*(3.99-x) = 0
0.25062657*x+8.9999999857 = 0
0.25062657*x+8.9999999857 = 0
0.25062657*x+8.9999999857 = 0 // - 8.9999999857
0.25062657*x = -8.9999999857 // : 0.25062657
x = -8.9999999857/0.25062657
x = -35.90999943
x = -35.90999943
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