$1/-4x^5(x^3-4x^2+7x-3)$
$=-4x^8+16x^7-28x^6+12x^5$
$2/3x^4(-2x^3+5x^2-\dfrac{2}{3}x+\dfrac{1}{3}$
$=-6x^7+15x^6-2x^5+x^4$
$3/-5x^2y^4(3x^2y^3-2x^3y^2-xy)$
$=-15x^4y^7+10x^5y^6+5x^3y^5$
$4/-3x^5y^7(\dfrac{2}{3}x^4y-y^3+\dfrac{1}{2})$
$=-2x^9y^8+3x^5y^10-\dfrac{3}{2}x^5y^7$
$5/\dfrac{1}{2}x^3y(2x^4y^3-4xy-6)$
$=x^7y^4-2x^4y^2-3x^3y$
$6/-\dfrac{5}{6}x(\dfrac{2}{3}x^2y+\dfrac{3}{4}xy^2-\dfrac{1}{2}xy$
$=-\dfrac{5}{9}x^3y-\dfrac{5}{8}x^2y^2+\dfrac{5}{12}x^2y$
$14/(\dfrac{1}{2}x+3)(2x^2-4x-6)$
$=x^3-2x^2-3x+6x^2-12x-18$
$=x^3+4x^2-15x-18$
$15/(\dfrac{3}{2}x-1)(3x^2-6x+9)$
$=\dfrac{9}{2}x^3-9x^2+\dfrac{27}{2}x-3x^2+6x-9$
$=\dfrac{9}{2}x^3-12x^2+\dfrac{39}{2}x-9$
$16/4x^2-(x+3)(x-5)+x$
$=4x^2-x^2+5x-3x+15+x$
$=3x^2+3x+15$
$17/4x(x^2-x-1)-(x^2-2)(x+3)$
$=4x^3-4x^2-4x-x^3-3x^2+2x+6$
$=3x^3-7x^2-2x+6$
$18/(x-5)(x+7)-x(x+3)(x-3)$
$=x^2+7x-5x-35-x(x^2-9)$
$=x^2+2x-35-x^3+9x$
$=-x^3+x^2+11x-35$
$20/\dfrac{1}{2}x-\dfrac{1}{3}y^2)(\dfrac{1}{2}x+\dfrac{1}{3}y^2)$
$=\dfrac{1}{4}x^2-\dfrac{1}{9}y^4$
