（a-b-c)-(2a+b+c)
=a-b-c-2a-b-c
= -(a+2b+2c)
= -[x的3次方-5x的平方+2(x的3次方-11x+6)+2(4x-3)]
= -(3x^3-5x^2-14x+6)
当x=-1时,（a-b-c)-(2a+b+c)= -(-3-5+14+6)= -12