3a+5b/5a+7b если 4a=-3b

4а = - 3b
a = - 3b : 4
a = - 0,75b
1) 3a + 5b = 3•( - 0,75b ) + 5b = - 2,25b + 5b = 2,75b
2) 5a + 7b = 5•( - 0,75b ) + 7b = - 3,75b + 7b = 3,25b
3) 2,75b : 3,25b = 2 3/4 : 3 1/4 = 11/4 : 13/4 = 11/13
Ответ 11/13

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