Ответы на вопрос:
Замена 7/x = a; y/5 = b { a + b = 28 { 1/a + 1/b = 5 подставляем 1 уравнение во 2 { b = 28 - a { 1/a + 1/(28-a) = 5 28 - a + a = 5a(28 - a) 28 + 5a^2 - 140a = 0 d/4 = 70^2 - 5*28 = 4900 - 140 = 4760 a1 = (70 - √4760)/5; b1 = 28 - a1 = (70 + √4760)/5 a2 = (70 + √4760)/5; b2 = 28 - a2 = (70 - √4760)/5 1) 7/x = a1 = (70-√4760)/5; x1 = 7*5/(70-√4760) = 35(70+√4760)/140 = = (70+√4760)/4 y/5 = b1 = (70+√4760)/5; y1 = (70+√4760) 2) аналогично 7/x = a2 = (70+√4760)/5; x2 = 7*5/(70+√4760) = (70-√4760)/4 y/5 = b2 = (70-√4760)/5; y2 = (70-√4760)
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