x²+8x+1+x²-9=02x²+8x-8=0x²+4x=4x²+4x+4=8(x+2)²=8x+2=±2√2x1=-2+2√2,x2=-2-2√2当x1=-2+2√2, 或x2=-2-2√2时,代数x²+8x+1与x²-9的值为相反数