(a+1/2b)²-(a-1/2b)²+(3a-b)(9a²+3ab+b²)=(a+1/2b+a-1/2b)(a+1/2b-a+1/2b)+(3a-b)(9a²+3ab+b²)=2ab+(3a-b)[(3a+b)²-3ab]∵ a=-1，b=2∴ ab=-2 3a+b=-1，3a-b=-5故原式=-4-5*(1+6) = -39
