已知等差数列﹛an﹜的前n项和为Sn,且a2+a9=10,则s10等于设等差数列﹛an﹜的公差为d,则S10=10a1+10×(10-1)﹨2d=10a1+45d又有a2+a9=10,得2a1+9d=10,
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![已知等差数列﹛an﹜的前n项和为Sn,且a2+a9=10,则s10等于设等差数列﹛an﹜的公差为d,则S10=10a1+10×(10-1)﹨2d=10a1+45d又有a2+a9=10,得2a1+9d=10,](/uploads/image/z/7227028-28-8.jpg?t=%E5%B7%B2%E7%9F%A5%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%EF%B9%9Ban%EF%B9%9C%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BASn%2C%E4%B8%94a2%2Ba9%3D10%2C%E5%88%99s10%E7%AD%89%E4%BA%8E%E8%AE%BE%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%EF%B9%9Ban%EF%B9%9C%E7%9A%84%E5%85%AC%E5%B7%AE%E4%B8%BAd%EF%BC%8C%E5%88%99S10%EF%BC%9D10a1%2B10%C3%97%EF%BC%8810-1%EF%BC%89%EF%B9%A82d%EF%BC%9D10a1%2B45d%E5%8F%88%E6%9C%89a2%2Ba9%EF%BC%9D10%EF%BC%8C%E5%BE%972a1%2B9d%EF%BC%9D10%EF%BC%8C)
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