-a(a²-2ab)-b(ab+2a²-b²),其中a=2,b=1/2

-a(a²-2ab)-b(ab+2a²-b²),其中a=2,b=1/2
-a(a²-2ab)-b(ab+2a²-b²),其中a=2,b=1/2

-a(a²-2ab)-b(ab+2a²-b²),其中a=2,b=1/2
-a(a²-2ab)-b(ab+2a²-b²)
= -a³+2a²b-ab²-2a²b+b³
= -a³-ab²+b³
= -2³-2×(1/2)²+(1/2)³
= -8-1/2+1/8
= -67/8