a) (2x^2-3x)(5x-2x+1) = (2x^2-3x)(3x+1) = 6x^3+2x^2-9x^2-3x
b) (x-2y)(3xy+5y^2+x) = 3x^2y+5xy^2+x^2-6xy^2-10y^3-2xy = 3x^y -xy^2 +x^2 -10y^3 -2xy
c) (x^2-25):(5-x)=(x+5)(x-5):(5-x) = -(x+5)(x-5):(x-5) = -x-5
d) (x^5+x^3+x^2+1):(x^3+1) = x^3(x^2+1)+(x^2+10:(x^3+1) = (x^3+1)(x^2+1) : ( x^3+1) = x^2 + 1