Toán Lớp 7: Tìm x,y,z biết:A, x-3/5-x=5/7 B, x-2/x-1=x+4/x+7

Question

Toán Lớp 7:  Tìm x,y,z biết:A, x-3/5-x=5/7 B, x-2/x-1=x+4/x+7

giangnguyen33 · Answer

Answer    a, {x-3}/{5-x} = 5/7   => 7 . (x - 3) = 5 . (5 - x)   => 7x - 21 = 25 - 5x   => 7x + 5x = 25 + 21   => 12x = 46   => x = 46 : 12   => x = 23/6   $ text{Vậy}$ x = 23/6   _________________   {x-2}/{x-1} = {x+4}/{x+7}   => (x - 2) . (x + 7) = (x - 1) . (x + 4)   => (x . x) + (x . 7) - (2 . x) - (2 . 7) = (x . x) + (x . 4) - (1 . x) - (1 . 4)   => x^{2} + 7x - 2x - 14 = x^{2} + 4x - x - 4   => x^{2} + 7x - 2x - 14 - x^{2} - 4x + x + 4 = 0   => (x^{2} - x^{2}) + (7x - 4x - 2x + x) + (-14 + 4) = 0   => 2x - 10 = 0   => 2x = 0 + 10   => 2x = 10   => x = 10 : 2   => x = 5   $ text{Vậy}$ x = 5

diemchau · Answer

A,x-$ frac{3}{5}$ -x=$ frac{5}{7}$    &hArr;(x-3).7=(5-x).5   &hArr;7x-21=25-5x   &hArr;7x+5x=25+21   &hArr;12x=46   &hArr;x=46:12   &hArr;$ frac{23}{6}$    Vậy x=$ frac{23}{6}$    B,$ frac{x-2}{x-1}$ =$ frac{x+4}{x+7}$    &hArr;(x-2).(x+7)=(x+4).(x-1)   &hArr;$x^{2}$ +7x-2x-14=$x^{2}$+4x-x-4   &hArr;$x^{2}$+5x-$x^{2}$-3x=-4+14   &hArr;2x=10   &hArr;x=10:2   &hArr;x=5   Vậy x=5