《新课程标准》强调“应重视口算,加强估算,鼓励算法多样化”.估算是相对计算而言,巧妙地利用估算可以很简炼地解答许多问题.一、利用有理数估算无理数的大致范围.“能用有理数估计一个无理数的大致范围”是“新课标”一项具体目标,近年的中考题对此有所反映.例1(2000年湖南长 The “New Curriculum Standards” emphasizes that “we should pay attention to oral calculations, strengthen estimation, and encourage the diversification of algorithms.” Estimates are relative calculations, and clever use of estimates can solve many problems in a concise manner. First, use rational numbers to estimate the approximate range of irrational numbers. “The use of rational numbers to estimate the approximate range of an irrational number” is a specific goal of the “new curriculum standard”. This has been reflected in the recent examination questions. Example 1 (2000 Hunan Province