(1) gen 11 约3.***,则：
a=9+gen11-12=gen11-3
b=9-gen11-5=4-gen11
(2)ab-3a+4b-7
=a*(b-3)+4*b-12+5
=a*(b-3)+4*(b-3)+5
=(a+4)*(b-3)+5
=(gen11-3+4)*(4-gen11-3)+5
=(gen11+1)*(1-gen11)+5
=1-(ge11)^2+5
=1-11+5
=-5
快乐生活.加油啦.额...谢谢