A=2a^3-2a^2+2a-1
B=3a^3-3a^2-4a-5
当a=-1/7时,
A-4(B-2/A+B)
=2a^3-2a^2+2a-1-4(3a^3-3a^2-4a-5-2/2a^3-2a^2+2a-1+3a^3-3a^2-4a-5)
=2a^3-2a^2+2a-5(3a^3-3a^2-4a-7/5a^3-5a^2-2a-6)
=2(-1/7)^3-2(-1/7)^2+2(-1/7)-5[3(-1/7)^3-3(-1/7)^2-4(-1/7)-7/5(-1/7)^3-5(-1/7)^2-2(-1/7)-6]
=2(-1/343)-2(1/49)+2(-1/7)-5[3(-1/343)-3(1/49)-4(-1/7)-7/5(-1/343)-5(1/49)-2(-1/7)-6]
=(-2/343)-(2/49)-(2/7)-5[(-3/343)-(3/49)+(4/7)-7/(-5/343)-(5/49)+ (2/7)-6]
=(-1829/343)[(-2229/343)/(-2000/343)]
=(-1829/343)(2229/2000)
=-5.943
正确答案是这样吗?