多项式(a+2)x*x+(9a+10b)xy-x+2y+7中的二次项为:(a+2)x*x和(9a+10b)xy,
依题意,得,
a+2=0,9a+10b=0,
解得a=-2,b=9/5
所以3a-5b
=3×(-2)-5×(9/5)
=-6-9
=-15
多项式(a+2)x*x+(9a+10b)xy-x+2y+7中的二次项为:(a+2)x*x和(9a+10b)xy,
依题意,得,
a+2=0,9a+10b=0,
解得a=-2,b=9/5
所以3a-5b
=3×(-2)-5×(9/5)
=-6-9
=-15