$\text{Đáp án+Giải thích các bước giải:}$
$a) [2(x-y)³-7(y-x)²-(y-x)]:(x-y)$
$= [2(x-y)³+7(x-y)²+(x-y)]:(x-y)$
$= 2(x-y)²+7(x-y)+1$
$b)$ [3$(x-y)^{5}$ -2$(x-y)^{4}$ $+3(x-y)²]$ $:[5(x-y)²]$
$= [3(x-y)³-2(x-y)²+3]:5$
$= [3(x³-3x²y+3xy²-y³)-2(x²-2xy+y²)+3]:5$
$= (3x³-9x²y+9xy²-3y³-2x²+4xy-2y²+3):5$