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在七年级学习“整式乘法公式”时,有这么一道选择题:下列各算式中,能用平方差公式计算的是()A(.-x-y)(x+y)B(.-x+y)(x-y)C(.-x-y)(x-y)D(.2x-y)(x+2y)对班级中下等学生而言,做起来就很有困难。从形式上,每一个算式都很接近平方差公式中的(a+b)(a-b),班级中各个选项都会出现。分析根源:学生对于完全平方公式、平方差公式、多项式乘多项式等算式的特点未能很好地把握。如果本题是计算题,有的学生可能都只用多项式乘多项式法则来计算结果。
In the seventh grade to learn “integer multiplication formula ”, there is a multiple choice question: the following formulas can be calculated using the square difference formula is () A (.- xy) (x + y) B + y) (xy) C (.- xy) (xy) D (.2x-y) (x + 2y) For undergraduates, it is difficult to do so. Formally, each of the formulas is very close to (a + b) (a-b) in the squared difference formula, and various options in the class appear. Analysis of the root causes: students for the full square formula, the square difference formula, polynomial polynomial equations and other characteristics of the failure to properly grasp. If this question is a calculation question, some students may only use polynomial polynomial rules to calculate the result.