(-a²b/2)(2a²/3-ab/2-b²)+a⁴b/3=-a⁴b/3+a³b²/4+a²b³/2+a⁴b/3=a³b²/4+a²b³/2=(a²b²/2)(a/2+b)因为a=1,b=-1/2所以原式=(a²b²/2)(a/2+b)=(1²*(-1/2)²/2)(1/2-1/2)=0
