初中数学题库八年级6.5:运用完全平方公式和提取公因式化简二次根式例题解析

初中数学题库八年级6.5:运用完全平方公式和提取公因式化简二次根式例题解析

例题1、化简:\(\displaystyle \left( {-\sqrt{2}+\sqrt{5}+\sqrt{3}} \right)\left( {\sqrt{2}+\sqrt{5}-\sqrt{3}} \right)\left( {\sqrt{2}-\sqrt{5}+\sqrt{3}} \right)\left( {\sqrt{2}+\sqrt{5}+\sqrt{3}} \right)\)

原式\(\displaystyle =\left[ {\sqrt{5}+\left( {\sqrt{3}-\sqrt{2}} \right)} \right]\left[ {\sqrt{5}-\left( {\sqrt{3}-\sqrt{2}} \right)} \right]\left[ {\left( {\sqrt{2}+\sqrt{3}} \right)-\sqrt{5}} \right]\left[ {\left( {\sqrt{2}+\sqrt{3}} \right)+\sqrt{5}} \right]\)

\(\displaystyle =\left[ {5-\left( {3+2-2\sqrt{6}} \right)} \right]\left[ {\left( {2+3+2\sqrt{6}} \right)-5} \right]\)

\(\displaystyle =2\sqrt{6}\times 2\sqrt{6}\)

\(\displaystyle =24\)

例题2、化简:\(\displaystyle {{\left( {2\sqrt{3}-\sqrt{{11}}} \right)}^{{16}}}{{\left( {2\sqrt{3}+\sqrt{{11}}} \right)}^{{17}}}\)

原式\(\displaystyle =\left[ {{{{\left( {2\sqrt{3}-\sqrt{{11}}} \right)}}^{{16}}}{{{\left( {2\sqrt{3}+\sqrt{{11}}} \right)}}^{{16}}}} \right]\left( {2\sqrt{3}+\sqrt{{11}}} \right)\)

\(\displaystyle ={{\left[ {\left( {2\sqrt{3}-\sqrt{{11}}} \right)\left( {2\sqrt{3}+\sqrt{{11}}} \right)} \right]}^{{16}}}\left( {2\sqrt{3}+\sqrt{{11}}} \right)\)

\(\displaystyle ={{1}^{{16}}}\left( {2\sqrt{3}+\sqrt{{11}}} \right)\)

\(\displaystyle =2\sqrt{3}+\sqrt{{11}}\)

例题3、化简:\(\displaystyle \left( {\sqrt{{15}}-2\sqrt{{10}}+\sqrt{{30}}} \right)\times \sqrt{5}\)

原式\(\displaystyle =\sqrt{{15}}\times \sqrt{5}-2\sqrt{{10}}\times \sqrt{5}+\sqrt{{30}}\times \sqrt{5}\)  ------------运用乘法分配律

\(\displaystyle =\sqrt{{75}}-2\sqrt{{50}}+5\sqrt{6}\)

\(\displaystyle =5\sqrt{3}-10\sqrt{2}+5\sqrt{6}\)

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