解
a²-a-4=0
a²-a=4
∴
a²-2(a²-a+3)-1/2(a²-a+4)-a
=a²-2a²+2a-6-1/2(4+4)-a
=-a²+2a-6-4-a
=-a²+a-10
=-(a²-a)-10
=-4-10
=-14