1-20根号顺口溜
二次根式不离二，方方面面各两个，两点非负要记清，a和根式它本身，两个公式要记好，化简帮你去根号，两条性质要记牢，根式变形要用到，两个概念要分清，判断之前先变形，两类运算最重要，试卷当中常考到。
两点非负，被开方数a是非负数，即a>=0，根号a本身是非负数，即根号a>=0
√1 = 1
√2 = 1.4142135623731
√3 = 1.73205080756888
√4 = 2
√5 = 2.23606797749979
√6 = 2.44948974278318
√7 = 2.64575131106459
√8 = 2.82842712474619
√9 = 3
√10 = 3.16227766016838
√11 = 3.3166247903554
√12 = 3.46410161513775
√13 = 3.60555127546399
√14 = 3.74165738677394
√15 = 3.87298334620742
√16 = 4
√17 = 4.12310562561766
√18 = 4.24264068711928
√19 = 4.35889894354067
√20 = 4.47213595499958
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