(a+b)(a+b)=a*a+2ab+b*b=8
所以,a*a+b*b=8-2ab
所以,8-2ab=50即2ab=-42,4ab=-84
(a+b)(a+b)-4ab=8+84
(a-b)(a-b)=92
a-b=根号92=2倍根号23