一.在三角形ABC中,a,b,c分别是角A,B,C的对边,且(a+b+c)(b+c-a)=3bc1.求角A的大小2.若a=根号3,b+c=3,求b和c的值二.设等差数列{an}的前n项和为Sn,已知a4=-25,S13=-2081.求数列{an}的通项公式2.求数列{an}的前n项和
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![一.在三角形ABC中,a,b,c分别是角A,B,C的对边,且(a+b+c)(b+c-a)=3bc1.求角A的大小2.若a=根号3,b+c=3,求b和c的值二.设等差数列{an}的前n项和为Sn,已知a4=-25,S13=-2081.求数列{an}的通项公式2.求数列{an}的前n项和](/uploads/image/z/5496331-67-1.jpg?t=%E4%B8%80.%E5%9C%A8%E4%B8%89%E8%A7%92%E5%BD%A2ABC%E4%B8%AD%2Ca%2Cb%2Cc%E5%88%86%E5%88%AB%E6%98%AF%E8%A7%92A%2CB%2CC%E7%9A%84%E5%AF%B9%E8%BE%B9%2C%E4%B8%94%28a%2Bb%2Bc%29%28b%2Bc-a%29%3D3bc1.%E6%B1%82%E8%A7%92A%E7%9A%84%E5%A4%A7%E5%B0%8F2.%E8%8B%A5a%3D%E6%A0%B9%E5%8F%B73%2Cb%2Bc%3D3%2C%E6%B1%82b%E5%92%8Cc%E7%9A%84%E5%80%BC%E4%BA%8C.%E8%AE%BE%E7%AD%89%E5%B7%AE%E6%95%B0%E5%88%97%7Ban%7D%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BASn%2C%E5%B7%B2%E7%9F%A5a4%3D-25%2CS13%3D-2081.%E6%B1%82%E6%95%B0%E5%88%97%7Ban%7D%E7%9A%84%E9%80%9A%E9%A1%B9%E5%85%AC%E5%BC%8F2.%E6%B1%82%E6%95%B0%E5%88%97%7Ban%7D%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C)
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