Toán Lớp 9: (2 căn 2-căn 30)x căn( 8 +căn 15)
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Toán Lớp 9: (2 căn 2-căn 30)x căn( 8 +căn 15)
Comments ( 1 )
\left( {2\sqrt 2 – \sqrt {30} } \right).\sqrt {8 + \sqrt {15} } \\
= \left( {2 – \sqrt {15} } \right).\sqrt 2 .\sqrt {8 + \sqrt {15} } \\
= \left( {2 – \sqrt {15} } \right).\sqrt {16 + 2.\sqrt {15} } \\
= \left( {2 – \sqrt {15} } \right).\sqrt {{{\left( {\sqrt {15} + 1} \right)}^2}} \\
= \left( {2 – \sqrt {15} } \right).\left( {\sqrt {15} + 1} \right)\\
= 2\sqrt {15} + 2 – 15 – \sqrt {15} \\
= \sqrt {15} – 13
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