解:a 2-a-4=0故 a 2-2(a 2-a +3)-?(a 2-a-4)-a= (a 2-a)-2(a 2-a +3)-?(a 2-a-4)=(a 2-a-4)+4-2(a 2-a -4+7)-?(a 2-a-4)=0+4-2×7-1/2×0=-10已知a 2-a-4=0a 2-a=4 a 2-2(a 2-a +3)-?(a 2-a-4)-a=a2-2a2+2a-6-1/2a2+1/2a+2-a=-3/2a2+3/2a-4=-3/2 *4-4=-10已知a2-a-4=0,则a2-a=4
a2-2(a2-a+3)-1/2(a2-a-4)-a
=a2-2(4+3)-1/2(4-4)-a
=a2-14-a
=a2-a-14
=4-14
=-10