上面还有一个x1+x2=1/a ：(x1+x2)/2+(ax1²-1+ax2²-1)/2=0x1+x2+a(x1²+x2²)-2=01/a+a[(x1+x2)²-2x1x2]-2=01/a+a(1/a²-2x1x2)-2=01/a+1/a-2a(x1x2)-2=02a(x1x2)=2-(2/a) x1x2=(2a-2)/(2a²) x1x2=(a-1)/a²
