/a-2/+/b+1/=0
/a-2/=0,/b+1/=0
a=2,b=-1
5a平方b-2ab平方+3ab
=ab(5a-2b+3)
=2*(-1)*[5*2-2*(-1)+3]
=-2*(10+2+3)
=-2*15
=-30