求5ab-4a²b²+8ab²-a²b+4a²b²的值,其中a=1,b=-1/2.

求5ab-4a²b²+8ab²-a²b+4a²b²的值,其中a=1,b=-1/2.
求5ab-4a²b²+8ab²-a²b+4a²b²的值,其中a=1,b=-1/2.

求5ab-4a²b²+8ab²-a²b+4a²b²的值,其中a=1,b=-1/2.
原式=5ab+8ab²-a²b
=5*1*(-1/2)+8*1*(-1/2)²-1²*(-1/2)
=-5/2+2+1/2
=0

=5ab+8ab^2-a^2b=ab(5+8b-a)=-1/2(5-4-1)=0