x²y-x²-y²x+y²=xy(x-y)-(x²-y²)=xy(x-y)-(x-y)(x+y)=(x-y)(xy-x-y)
10-5-2=3 часа x время по течению
(6-2)*(3-x)=(6+2)*x 12-4x=8x 12x=12 x=1(час) Расстояние 8км/ч*1ч=8км
x²y-x²-y²x+y²=xy(x-y)-(x²-y²)=xy(x-y)-(x-y)(x+y)=(x-y)(xy-x-y)