若{a_n}是一个各项都为正数的无穷递增等比数列，a₁和a₃是方程x²﹣5x+4=0的两个根，求此数列的通项公式a_n与前n项和S_n．

    Hello, my name is Gina. John, Anna and I are good friends. We are in the same grade (年级). But they are in Class Five and I am in Class Three. We get up at 7:00 and go to school at 7:30. In the morning we have four lessons. We have English every morning. John and Anna have English at 10:00 in the morning and I have it at 11:00. English is my favorite subject. Math is their favorite. And we all like P.E.

    In the afternoon, we have three lessons. At 2:30 we have the art lesson in the same classroom. After school we often play soccer. We all like soccer. Sometimes (有时) we watch TV at my house. We don't play any computer games.

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