1)60:3\5=60*5\3=100км\ч-скорость поезда.
2)68:17\30=68*30\17=120км\ч-скорость остального пути.
<span>3)120-100=на 20км\ч больше-стала скорость.</span>
1,5-0,5(1,5+0,5)/2*1,5-0,5=0,5/2,5=1/5=0,2
(7х-8)/(5х+5) + (4-5х)/(3х+3) =
= (7х-8)(3х+3)/(5х+5)(3х+3) + (4-5х)(5х+5)/(5х+5)(3х+3) =
= (21х²+21х-24х-24)/(5х+5)(3х+3) + (20х+20-25х²-25х)/(5х+5)(3х+3) =
= (21х²+21х-24х-24 + 20х+20-25х²-25х)/(5(х+1)*3(х+1)) =
= (-4х²-8х-4)/(15(х+1)²) = -4(х²+2х+1)/(15(х+1)²) = -4(х+1)² / (15(х+1)²) = -4/15,
то есть данное выражение не зависит от переменной х
((x+y)/x-2x/(x-y))×((y-x)/(x²+y²))=((x+y)(x-y)-2x²)/(x*(x-y))×((y-x)/(x²+y²))=
=((x²-y²-2x²)/(x*(x-y))×((y-x)/(x²+y²))=((-x²-y²)/(x*(x-y))×((y-x)/(x²+y²))=
=((x²+y²)/(x*(y-x))×((y-x)/(x²+y²))≡1/x.