已知 x1,x2{x}_{1},{x}_{2}x1,x2 是实数，满足 x12+8x22−4x1x2=8{x}_{1}^{2} + 8{x}_{2}^{2} - 4{x}_{1}{x}_{2} = 8x12+8x22−4x1x2=8 ，当 ∣x1∣\left| {x}_{1}\right|∣x1∣ 取得最大值时, ∣x1+x2∣=\left| {{x}_{1} + {x}_{2}}\right| =∣x1+x2∣= ___.