《13.1平方根》课件(人教版八年级上).ppt

Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. ?? 93 2??25 4 2?x一、情境导入:如果一个数的平方等于 9, 这个数是多少? 讨论:这样的数有两个,它们是 3和-3. 注意中括号的作用. ,则 x等于多少呢? 又如: x 2 25 4x 1163649 填表: ±1 ±4 ±6 ±7 5 2? Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. 二、感受新知: 1、平方根的概念:如果一个数的平方等于 a, 那么这个数就叫做 a的___________ 或_______ . 即:如果 2x=a,那么 x叫做_____________ . 求一个数的平方根的运算,叫做_______ . ?例如±3的平方等于 9,9的平方根是±3, 所以平方与开平方互为逆运算. 平方根二次方根 a的平方根开平方 Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright 2004-2011 Aspose Pty Ltd. Copyright 2004-2011 Aspose Pty Ltd. 2.、观察:课本 P73 的图 -2. 图 -2 中的两个图描述了平方与开平方互为逆运算的运算过程,揭示了开平方运算的本质并根据这个关系说出 1,4,9 的平方根. 1的平方根是±14的平方根是±2 ±9的平方根是±3 Evaluation only. Evaluation only. Created with Client Profile . Created with Client Profile . Copyright