作业讲评是课堂教学中的一个重要环节.通过作业讲评,既可以帮助学生复习所学知识,澄清某些方面的模糊认识,又能提升学生的思维能力.下面是笔者在一次作业讲评课中的一些做法,恳请同仁们斧正!题目已知二次函数f(x)=ax~2-(a+2)x+1,若a>0,试判断函数f(x)在(-2,-1)上是否有零点?思路1:抛物线的对称轴x=a+2/2a>0,开口向上.因为f(0)=1>0,所以函数f(x)在(-2,-1)上没有零点.点评:这是个简洁、明快的证法,言简意赅,通俗 Homework assessment is an important part of classroom teaching through homework reviews, both to help students review their knowledge, to clarify some aspects of vague understanding, but also enhance students’ thinking ability. The following is the author in a homework comment class The problem is known quadratic function f (x) = ax ~ 2- (a +2) x +1, if a> 0, try to determine the function f (x) in the (-2, - 1) is there a zero point? Idea 1: The symmetry axis of the parabola is x = a + 2 / 2a> 0 and the opening is upward. Since f (0) = 1> 0, There is no zero. Comments: This is a concise, bright card method, concise, popular