<span>x+y=6 y = 6 - x y=6-x</span>
А что вы здесь имели ввиду?
1) (<span>x-6)/(x-8)=3/2 </span>
<span> 2х - 12 = 3х - 24</span>
<span> -х = - 12</span>
<span> х = 12</span>
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<span>2) <span>x-6/x-8=3/2</span></span>
<span><span> (x^2-6) /x = 8+ 3/2</span></span>
<span><span> (x^2 - 6)/ x = 19/2</span></span>
<span><span> 2x^2 - 12 = 19x</span></span>
<span><span> 2x^2 - 19x - 12 = 0</span></span>
<span><span>D = 361 +96 = 467</span></span>
<span><span>x 1 = ( 19+ sqrt(467) ) / 4</span></span>
<span><span>x2 = (19 - sqrt(467) ) / 4</span></span>