(ax^2+bx+1)( 2x^2-3x+1)=2a x^4+(2b-3a)x^3+(a-3b+2) x^2+(b-3)x+1
∵展开式中不含x^3和项含x^3项
∴2b-3a=0,b-3=0
解得：b=3,a=2