1)5x/(x-10) + 20x/(x-10)²=(5x²-50x+20x)/(x-10)²=(5x²-30x)/(x-10)²=5x(x-6)/(x-10)²
2)5x(x-6)/(x-10)² : 4(x-6)/(x-10)(x+10)=5x(x-6)/(x-10)² * (x-10)(x+10)/4(x-6)=
=5x(x+10)/4(x-10)
3)5x(x+10)/4(x-10) -25x/(x-10)=(5x²+50x-25x)/(x-10)=(5x²+25x)/(x-10)=5x(x+5)/(x-10)
за х км/час примем собственную скорость теплохода;
(3а-1)(3а+1)-(3а-1)^2= 9a^2 +3a-3a-1-9a^-1+6a=6a-2.