①若α为某三角形的一个内角,且tanα=—5/12,则cosα等于?②记等比数列{an}的前n项和为Sn,若S3=2,S6=18,则S10/S5=?③直线L与圆O:χ²+Y²+2x-4y+a=0(a<3)相交于A,B两点,若弦AB的中点为P(-2,3)
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![①若α为某三角形的一个内角,且tanα=—5/12,则cosα等于?②记等比数列{an}的前n项和为Sn,若S3=2,S6=18,则S10/S5=?③直线L与圆O:χ²+Y²+2x-4y+a=0(a<3)相交于A,B两点,若弦AB的中点为P(-2,3)](/uploads/image/z/1584638-62-8.jpg?t=%E2%91%A0%E8%8B%A5%CE%B1%E4%B8%BA%E6%9F%90%E4%B8%89%E8%A7%92%E5%BD%A2%E7%9A%84%E4%B8%80%E4%B8%AA%E5%86%85%E8%A7%92%2C%E4%B8%94tan%CE%B1%3D%E2%80%945%2F12%2C%E5%88%99cos%CE%B1%E7%AD%89%E4%BA%8E%3F%E2%91%A1%E8%AE%B0%E7%AD%89%E6%AF%94%E6%95%B0%E5%88%97%EF%BD%9Ban%EF%BD%9D%E7%9A%84%E5%89%8Dn%E9%A1%B9%E5%92%8C%E4%B8%BASn%2C%E8%8B%A5S3%3D2%2CS6%3D18%2C%E5%88%99S10%2FS5%3D%3F%E2%91%A2%E7%9B%B4%E7%BA%BFL%E4%B8%8E%E5%9C%86O%EF%BC%9A%CF%87%26sup2%3B%EF%BC%8BY%26sup2%3B%2B2x-4y%2Ba%3D0%EF%BC%88a%EF%BC%9C3%EF%BC%89%E7%9B%B8%E4%BA%A4%E4%BA%8EA%2CB%E4%B8%A4%E7%82%B9%2C%E8%8B%A5%E5%BC%A6AB%E7%9A%84%E4%B8%AD%E7%82%B9%E4%B8%BAP%EF%BC%88-2%2C3%EF%BC%89)
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