∵a²+4a-4=0时
(a+2)²=8
a+2=±√8
a1=-2+2√2 a2=-2-2√2
∴a²+12a-5=(a²+4a-4)+8a-1=8a-1
当a=-2+2√2时,原式=-16+16√2
当a=-2-2√2时,原式=-16-16√2