(m + n)³ - m² - 2mn - n² = (m + n)³ - (m² + 2mn + n²) = (m + n)³ - (m + n)² =
= (m + n)²(m + n - 1) = (m + n)(m + n)(m + n - 1)
x-скорость течение реки
<span>33/(20+х)=27/(20-х)</span>
<span>х=2 </span>
<span>33/22+27/18=3ч </span><span>Время в пути</span>
Вот.......................................
9+6+8x=3x-3
8x-3x=-3-9-6
5x=-18
x=-18/5