4x的平方+3xy-x的平方-3xy+9
=4x的平方-x的平方+3xy-3xy+9
=3x的平方+9
=3*(-2)的平方+9
=3*4+9
=12+9
=21
3-[3（x+2y）-2（x-1）]
=3-(3x+6y-2x+2)
=3-3x-6y+2x-2
=3-2-3x+2x-6y
=1-x-6y
=1-(-1)-6*(-1/3)
=1+1+2
=4