8) a) 2x•10y^2–3x•4xy+2xy•5x =
= 20xy^2–12x^2y+10x^2y =
= 20xy^2–2x^2y = 2xy(10y–x)
б) х(3у–1)–у(х–3)–2(ху–х+у) =
= 3ху–х–ху+3у–2ху+2х–2у = х+у
в) 3(а^2–а+3)–0,5а(4а–6) =
=3а^2–3а+9–2а^2+3а = а^2+9
9) 3а^3+а^5+10+4а^3–4–а^5–5а^3=
=2а^3+6=2*(-1000)+6=–1994
10) 3х^2–7х+11+х^2–3х+7=
= 4х^2–10х+18
11) а) 5х^3у+15х^3=5х^3(у+3)
б) 7а(а+b)–6(a+b)=(a+b)(7a–6)
в) 3(y–2)–x(2–y)=3(y–2)+x(y–2)=
=(y–2)(3+x)