22.2x^2y-[(-3x^2y^2+3x^2y)+(3x^2y^2-3xy^2)]
=2x^2y+3x^2y^2-3x^2y-3x^2y^2+3xy^2
=2x^2y-3x^2y+3x^2y^2-3x^2y^2+3xy^2
=-x^2y+3xy^2
=xy(-x+3y)
其中x=－1,y=0.5得xy(-x+3y)=-0.5(1.5+1)=-0.5X2.5=-1.25
23.A=3a^2b+3ab^2+4
B=a^2b+11ab^2+a^4
C=-8ab^2+2a^2b+c^4
A+B-C
=3a^2b+3ab^2+4+a^2b+11ab^2+a^4-(-8ab^2+2a^2b+c^4)
=3a^2b+3ab^2+4+a^2b+11ab^2+a^4+8ab^2-2a^2b-c^4
=2a^2b+22ab^2+a^4-c^4+4 =2ab(a+11b)+(a^2+c^2)(a-c)(a+c)+4
,当a=－1,b=1,c=2时 原式=-20+5x(-3)+4=-31
24.2x^3-x^2+x-1+3x^3+2mx^2-5x+3
=5x^3+(2m-1)x^2-4x+2
要不含二次项,则2m-1=0即m=1/2