已知A=a³-3a²+2a-1,B=2a³+2a²-4a-5.当a=-1时,求3A-2[2B+(A-B)/2]的值.
问题描述:
已知A=a³-3a²+2a-1,B=2a³+2a²-4a-5.当a=-1时,求3A-2[2B+(A-B)/2]的值.
答
3A-2[2B+(A-B)/2]=3A-4B-A+B=2A-3B=2(a³-3a²+2a-1)-3(2a³+2a²-4a-5)=(2a³-6a²+4a-2)-(6a³+6a²-12a-15)=-4a³-12a²+16a+13=4-12-16+13=-11