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在“乘法口诀”的教学中,一般只要求学生理解“小九九”口诀表,能对口诀表横着背(从左往右)、竖着背,拐弯背。然而,由于表中45句口诀,全部是小数在前,大数在后,无论学生背得怎样熟练,都不可避免地存在两个弊病:其一,在乘除法计算中,遇到需要大数在前,小数在后的口诀时,学生必须先在思想上把这个口诀转化为小数在前,大数在后的口诀,然后,再从口诀表中选用,影响了计算速度。其二,学生只熟悉小数在前,大数在后的乘法口诀,无论在实际生活中,还是在思维过程中,都显得简单、单一,不利于学生思维能力和解决实际问题能力的发展。(尤其是逆向思维能力)针对这些情况,我在教学乘法口诀中注意让学生进行逆向思维的训练,掌握规律,灵活应用乘
In the “multiplication formula” teaching, generally only requires students to understand the “small ninety-nine” formulas table, the table can be horizontal (from left to right), vertical back, turning back. However, because of the 45 formulas in the table, all the decimals are in the front. After the large numbers are behind, no matter how skilled the students are, inevitably there are two disadvantages: First, in the calculation of multiplication and division, Before and after the decimal formulas, students must first think of this formula into the decimal in front, after the majority of formulas, and then from the table of tactics, affecting the calculation speed. Second, students are only familiar with decimals in front, after the majority of the multiplication formulas, both in real life, or in the thinking process, are simple, single, is not conducive to students' thinking ability and ability to solve practical problems. (Especially the ability of reverse thinking) In view of these situations, I pay attention to students in the teaching multiplication formulas to train students to reverse thinking, master the law, flexible application of multiplication