a) (2x2+1)(x2+3)= 2x2(x2+3)+1(x2+3)=
=2x4+6x2+x2+3= 2x4+7x2+3
b) (3x3+2)(x3−4)= 3x3(x3−4)+2(x3−4)=
=3x6−12x3+2x3−8= 3x6−10x3−8
c) 2(a+3)(3a−2)= (2a+6)(3a−2)=
=2a(3a−2)+6(3a−2)=
=6a2−4a+18a−12= 6a2+14a−12
d) (3a2−b)(a2−2b)= 3a2(a2−2b)−b(a2−2b)=
=3a4−6a2b−a2b+2b2= 3a4−7a2b+2b2
e) (−a3+2b)(2a3−b)= −a3(2a3−b)+2b(2a3−b)=
=−2a6+a3b+4a3b−2b2= −2a6+5a3b−2b2
f) −4(a−2b)(2b−a)= (−4a+8b)(2b−a)=
=−4a(2b−a)+8b(2b−a)=
=−8ab+4a2+16b2−8ab= 4a2+16b2−16ab
g) (2x2−3y2)(2x2+3y2)= 2x2(2x2+3y2)−3y2(2x2+3y2)=
=4x4+6x2y2−6x2y2−9y4= 4x4−9y4
h) (−x3+4y3)(3x3−2y)= −x3(3x3−2y)+4y3(3x3−2y)=
=−3x6+2x3y+12x3y3−8y4
i) −3(x−2y2)(y−x2)= (−3x+6y2)(y−x2)=
=−3x(y−x2)+6y2(y−x2)=
=−3xy+3x3+6y3−6x2y2