初一答题PPT
题目1下列各式中正确的是 ( )A. 7a - a = 6 B. $a^{2} \cdot a^{4} = a^{6}$ C. $a^{6} \div a...
题目1下列各式中正确的是 ( )A. 7a - a = 6 B. $a^{2} \cdot a^{4} = a^{6}$ C. $a^{6} \div a^{2} = a^{3}$ D. $2a^{-2} = \frac{1}{4a^{2}}$答案B解析A. $7a - a = 6a$，故A错误；B. $a^{2} \cdot a^{4} = a^{6}$，故B正确；C. $a^{6} \div a^{2} = a^{4}$，故C错误；D. $2a^{-2} = \frac{2}{a^{2}}$，故D错误．故选B．题目2下列各式中正确的是 ( )A. $(x - 1)^{2} = x^{2} - 1$ B. $(x + 1)^{2} = x^{2} + 2x + 1$C. $(x - 3)^{2} = x^{2} - 6x + 9$ D. $(x + 2)^{2} = x^{2} + 4x + 4$答案D解析A. $(x - 1)^{2} = x^{2} - 2x + 1$，故本选项错误；B. $(x + 1)^{2} = x^{2} + 2x + 1$，故本选项正确；C. $(x - 3)^{2} = x^{2} - 6x + 9$，故本选项错误；D. $(x + 2)^{2} = x^{2} + 4x + 4$，故本选项正确．故选D．题目3下列计算正确的是 ( )A. $3a + 2b = 5ab$ B. $5a^{2} - 2b^{2} = 3$C. $7x + 5x = 21x^{2}$ D. $4y^{2} - 4y^{2} = 0$答案D解析A. $3a + 2b$ 不能合并，故本选项错误；B. $5a^{2} - 2b^{2}$ 不能合并，故本选项错误；C. $7x + 5x = 12x$，故本选项错误；D. $4y^{2} - 4y^{2} = 0$，正确．故选D．题目4下列各式中正确的是 ( )A. $a^{6} \div a^{2} = a^{3}$ B. $a^{2} \cdot a^{4} = a^{6}$C. $2a^{-2} = \frac{1}{4a^{2}}$ D. $7a - a = 6$答案B解析A. $a^{6} \div a^{2} = a^{4}$，故A错误；B. $a^{2} \cdot a^{4} = a^{6}$，故B正确；C. $2a^{-2} = \frac{2}{a^{2}}$，故C错误；D. $7a - a = 6a$，故D错误．故选B．题目5下列各式中正确的是 ( )A. $3a + 2b = 5ab$ B. $5a^{2} - 2b^{2} = 3$C. $7x + 5x = 21x^{2}$ D. $4y^{2} - 4y^{2} = 0$答案D解析A. $3a + 2b$ 不能合并，故本选项错误；B. $5a^{2} - 2b^{2}$ 不能合并，故本选项错误；C. $7x + 5x = 12x$，故本选项错误；D. $4y^{2} - 4y^{2} = 0$，正确．故选D．题目6下列计算正确的是 ( )A. $3a + 2b = 5ab$ B. $5a^{2} - 2b^{2} = 3$C. $7x + 5x = 21x^{2}$ D. $4y^{2} - 4y^{2} = 0$答案D解析A. $3a + 2b$ 不能合并，故本选项错误；B. $5a^{2} - 2b^{2}$ 不能合并，故本选项错误；C. $7x + 5x = 12x$，故本选项错误；D. $4y^{2} - 4y^{2} = 0$，正确．故选D．题目7下列各式中正确的是 ( )A. $3a + 2b = 5ab$ B. $5a^{2} - 2b^{2} = 3$C. $7x + 5x = 21x^{2}$ D. $4y^{2} - 4y^{2} = 0$答案D解析A. $3a$ 和 $2b$ 不是同类项，因此不能合并，故本选项错误；B. $5a^{2}$ 和 $2b^{2}$ 不是同类项，因此不能合并，故本选项错误；C. $7x + 5x = 12x$，与给定的等式不相符，故本选项错误；D. $4y^{2} - 4y^{2} = 0$，与给定的等式相符，故本选项正确．故选D．
