初中数学题库八年级6.4:二次根式中完全平方公式的运用技巧案例解析

初中数学题库八年级6.4:二次根式中完全平方公式的运用技巧案例解析

例题1:化简:\(\displaystyle \frac{1}{{1-\sqrt[4]{3}}}+\frac{1}{{1+\sqrt[4]{3}}}+\frac{1}{{1+\sqrt{3}}}\)

原式\(\displaystyle =\frac{{1+\sqrt[4]{3}}}{{\left( {1-\sqrt[4]{3}} \right)\left( {1+\sqrt[4]{3}} \right)}}+\frac{{1-\sqrt[4]{3}}}{{\left( {1-\sqrt[4]{3}} \right)\left( {1+\sqrt[4]{3}} \right)}}+\frac{1}{{1+\sqrt{3}}}\)

\(\displaystyle =\frac{{1+\sqrt[4]{3}}}{{1-\sqrt{3}}}+\frac{{1-\sqrt[4]{3}}}{{1-\sqrt{3}}}+\frac{1}{{1+\sqrt{3}}}\)

\(\displaystyle =\frac{1}{{1-\sqrt{3}}}+\frac{1}{{1+\sqrt{3}}}\)

\(\displaystyle =\frac{{2\left( {1+\sqrt{3}} \right)+2\left( {1-\sqrt{3}} \right)}}{{\left( {1+\sqrt{3}} \right)\left( {1-\sqrt{3}} \right)}}\)

\(\displaystyle =\frac{{-4}}{{1-3}}\)

\(\displaystyle =2\)

例题2:化简:\(\displaystyle \left( {5+\sqrt{6}} \right)\left( {5\sqrt{2}-2\sqrt{3}} \right)\)

原式\(\displaystyle =\left( {5+\sqrt{6}} \right)\sqrt{2}\left( {5-\sqrt{6}} \right)\)

\(\displaystyle =\sqrt{2}\left( {25-6} \right)\)

\(\displaystyle =19\sqrt{2}\)

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