a) (2x+y)(x+2y)= 2x(x+2y)+y(x+2y)=
=2x2+4xy+xy+2y2=2x2+5xy+2y2
b) (2x+y)(x−2y)= 2x(x−2y)+y(x−2y)=
=2x2−4xy+xy−2y2= 2x2−3xy−2y2
c) (a−2b)(a+2b)=a(a+2b)−2b(a+2b)=
=a2+2ab−2ab−4b2=a2−4b2
d) (3n−2)(n−6)=3n(n−6)−2(n−6)=
=3n2−18n−2n+12= 3n2−20n+12
e) (x+2y+3)(x−2)=(x+2y+3)⋅x+(x+2y+3)⋅(−2)=
=x2+2xy+3x−2x−4y−6= x2+2xy+x−4y−6
f) (2a−b+c)(2a−3b)= (2a−b+c)⋅2a+(2a−b+c)⋅(−3b)=
=4a2−2ab+2ac−6ab+3b2−3bc= 4a2−8ab+2ac+3b2−3bc
g) (a+2b−3c)(2a−3b)= (a+2b−3c)⋅2a+(a+2b−3c)⋅(−3b)=
=2a2+4ab−6ac−3ab−6b2+9bc= 2a2+ab−6ac−6b2+9bc
h) −4(x+3)(x−2)= (−4x−12)(x−2)= −4x(x−2)−12(x−2)=
=−4x2+8x−12x+24= −4x2−4x+24
i) 2n(n−2m)(3+m)= (2n2−4nm)(3+m)=
=2n2(3+m)−4nm(3+m)= 6n2+2n2m−12nm−4nm2
