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许多有经验的教师对新课的引入都是很讲究的。一位老师在初二代数中讲“分母有理化”,先出了一道简单的计算题,让学生作为课堂练习: 计算1/(2~(1/2))(精确到0.01)。她指定两个小组的同学先求出2的算术平方根1.414……,然后直接除,另两组同学将分子、分母同乘2~(1/2)后再算。并叫两位同学分别用两法板演: 两法相比,优劣明显。教师说:“我们今天就讲这种(指乙的板演)简化根式运算的方法——分母有理化!”从而引入新课。另一位老师讲“数学归纳法”,先用一般归纳法引出一个日常生活中的正确判断(例略),再用一般归纳法引出“一切物质热胀冷缩”的错误判断,由此说明:若所论对象个数有限时,一般归纳法往
Many experienced teachers are very particular about the introduction of new courses. One teacher said “denominator rationalization” in the second-generation algebra, first came up with a simple calculation question for students to practice as a class: calculate 1 / (2 ~ (1/2)) (accurate to 0.01). She designated two groups of students first to find the arithmetic square root of 2 1.414 ......, and then in addition to the other two groups of students, the same numerator and denominator by 2 ~ (1/2) and then count. And called the two classmates were used to perform two panels: two laws, the advantages and disadvantages are obvious. The teacher said: “Today we talk about this method of simplifying the root-mean-square denominator!” Another teacher said “mathematical induction”, the first general inductive lead to a correct judgment of daily life (example), and then lead to the general induction of “all material thermal expansion and contraction,” the wrong judgment, indicating that : If the number of objects in the discussion is limited, the general induction method