答案与解析: (1)首项是38,末项是65,10项,是等差数列,公差是3 (2)首项是1,末项是45,7项 (3)首项是80,末项是45,8项,是等差数列,公差是5 (4)首项是2,末项是100,50项,是等差数列,公差是2