笔者听一位青年教师的“二次根式的加减”新授课.在“自主学习,复习引入”环节,教师设计了这样一道题目:下列计算是否正确,如不正确,请改正.1/33a~(1/2)-1/22a~(1/2)=a~(1/2)-a~(1/2)=0.答案一目了然,不正确,但大部分学生不知怎么改.教师解答如下:不正确.1/33a~(1/2)-1/22a~(1/2)=1/33~(1/2)·a~(1/2)-1/22~(1/2)·a~(1/2)=(3~(1/2)/3-2~(1/2)/2)a~(1/2).教师的意图可能是分别将3a~(1/2),2a~(1/2)拆开,以便 The author listens to a young teacher “secondary root addition ” new teaching In “independent study, review introduction ” link, the teacher designed such a topic: The following calculation is correct, if not correct, please correct .1 / 33a ~ (1/2) -1 / 22a ~ (1/2) = a ~ (1/2) -a ~ (1/2) = 0. The answer is clear at a glance, not correct, but most students do not know How to change the teacher to answer the following: incorrect .1 / 33a ~ (1/2) -1 / 22a ~ (1/2) = 1/33 ~ (1/2) · a ~ (1/2) -1 / 22 ~ (1/2) · a ~ (1/2) = (3 ~ (1/2) / 3-2 ~ (1/2) / 2) a ~ (1/2) The teacher’s intention may be Separate 3a ~ (1/2), 2a ~ (1/2), respectively