Odpowiedź:
a) (2b+a)(3-b)= 6b-2b2+3a-ab
b) (-x+3xy)(3-b)= -3x+xb+9xy-3xyb
c) (st-3)(5+st)= 5st+st2-15-3st= st2+2st-15
d) (2a-b)(a-2b)= 2a2-4ab-ab+2b2= 2b2+2a2-3ab
e) (m-n)(n-m)= mn-m2-n2+mn= -m2-n2+2mn
f) (-2a+k)(2k+3a)= -4ak-6a2+2k2+3ak= -6a2+2k2-ak
g) (z+3x)(2z+1)= 2z2+z+3zx+3x
h) (-4-k)(-2k+2y)= 8k-8y+2k2-2ky
i) (1-x)(1+3y)= 1+3y-x-3xy
