观察下列各式:=3×1-l=2,=3×2-l=5,=3×3-1=8,
=3×4-1=11,……按此规律:
(1)=_________________________________,=__________________________;
(2)写出的公式:=____________________;
观察下列各式:=3×1-l=2,=3×2-l=5,=3×3-1=8,
=3×4-1=11,……按此规律:
(1)=_________________________________,=__________________________;
(2)写出的公式:=____________________;