令a=1.345 2a=2.69 a-1=0.345
则原式为a×(a-1)×2a-a²-2a×(a-1)²
=2a³-2a²-a²-2a³+4a²-2a
=(a²-2a+1)-1
=(a-1)²-1
=0.345²-1
=-0.880975