“省略括号和加号”的教学内容安排在《有理数加减混合运算》这一节(人教版)。引入负数后,有理数的加减混合运算可以统一为加法运算。然而这“小小”的变化,却导致作业的错误率陡然上升。一、“省略”背后的问题1.符号的混乱。在“省略”之前,加减算式里,不仅有括号还有运算符号和性质符号,其中性质符号在括号内,运算符号在括号外,此时学生对每个运算的算理清清楚楚、明明白白。可“省略”之后,一个式子两种读法,式子中的“+”、“-”时而代 Teaching of “omission of parentheses and plus signs” is arranged in the section of “rational addition and subtraction of mixed numbers” (PEP). After the introduction of negative numbers, the addition and subtraction of rational numbers mixed operation can be unified for the addition. However, this “small” changes, but led to a sharp rise in the error rate of homework. A, “Omitted ” The problem behind 1. Symbols of chaos. In the “omitted” before the addition and subtraction formula, not only the brackets as well as arithmetic symbols and nature symbols, character symbols in parentheses, arithmetic symbols in the brackets, then the arithmetic operator for each operation is clear ,clear and direct. Can be “omitted ” after an expression of two kinds of reading, the formula of “+ ”, “- ” from time to time