设首项为a1,公差为d
则：
a2=a1+d,a8=a1+7d
a3=a1+2d,a7=a1+6d
由题得：(a1+d)+(a1+7d)=16
(a1+2d)(a1+6d)=48
解得：a1=0,d=2或a1=16,d=-2
当d=0
可求得：n