等腰三角形是一种特殊的三角形,它的性质在平面几何中有广泛的应用.但是,有的同学由于忽视条件,考虑问题不周,解题时常产生这样或那样的错误.一忽视三角形存在的条件例1一个等腰三角形的一边长为6,另一边长为12,求它的周长.错解:(1)当腰长为12时,周长为12×2+6=30;(2)当腰长为6时,周长为6×2+12=24.因此,这个等腰三角形的周长为30或 Isosceles triangle is a special triangle, its properties in the plane geometry has a wide range of applications, but some students due to neglect of conditions, consider the problem is not solved, problems often have one or the same error .On ignore the existence of the triangle Example 1 An isosceles triangle on one side of the length of 6, the other side of the length of 12, seeking its perimeter. Misinterpreted: (1) when the waist length of 12, the circumference of 12 × 2 +6 = 30; (2) When the waist length is 6, the circumference is 6 × 2 + 12 = 24. Therefore, the circumference of this isosceles triangle is 30 or