Toán Lớp 9: a) 4căn3 + căn27 – căn45 + căn5 b) ( căn28 – căn12 – căn7 ) . căn7 + 2căn21
c) căn9a – căn32a + căn49a – căn8a d) 2căn3 + căn( căn3-2)^2
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Toán Lớp 9: a) 4căn3 + căn27 – căn45 + căn5 b) ( căn28 – căn12 – căn7 ) . căn7 + 2căn21
c) căn9a – căn32a + căn49a – căn8a d) 2căn3 + căn( căn3-2)^2
MIK CẦN KẾT QUẢ ĐÚNG Ạ
Comments ( 1 )
a,\\
7\sqrt 3 – 2\sqrt 5 \\
b,\\
7\\
c,\\
10\sqrt a – 6\sqrt {2a} \\
d,\\
2 + \sqrt 3
\end{array}\)
a,\\
4\sqrt 3 + \sqrt {27} – \sqrt {45} + \sqrt 5 \\
= 4\sqrt 3 + \sqrt {9.3} – \sqrt {9.5} + \sqrt 5 \\
= 4\sqrt 3 + \sqrt {{3^2}.3} – \sqrt {{3^2}.5} + \sqrt 5 \\
= 4\sqrt 3 + 3\sqrt 3 – 3\sqrt 5 + \sqrt 5 \\
= 7\sqrt 3 – 2\sqrt 5 \\
b,\\
\left( {\sqrt {28} – \sqrt {12} – \sqrt 7 } \right).\sqrt 7 + 2\sqrt {21} \\
= \left( {\sqrt {4.7} – \sqrt {4.3} – \sqrt 7 } \right).\sqrt 7 + 2\sqrt {21} \\
= \left( {\sqrt {{2^2}.7} – \sqrt {{2^2}.3} – \sqrt 7 } \right).\sqrt 7 + 2\sqrt {21} \\
= \left( {2\sqrt 7 – 2\sqrt 3 – \sqrt 7 } \right).\sqrt 7 + 2\sqrt {21} \\
= \left( {\sqrt 7 – 2\sqrt 3 } \right).\sqrt 7 + 2\sqrt {21} \\
= {\sqrt 7 ^2} – 2\sqrt 3 .\sqrt 7 + 2\sqrt {21} \\
= 7 – 2\sqrt {3.7} + 2\sqrt {21} \\
= 7 – 2\sqrt {21} + 2\sqrt {21} \\
= 7\\
c,\\
\sqrt {9a} – \sqrt {32a} + \sqrt {49a} – \sqrt {8a} \\
= \sqrt {{3^2}.a} – \sqrt {{4^2}.2a} + \sqrt {{7^2}.a} – \sqrt {{2^2}.2a} \\
= 3\sqrt a – 4\sqrt {2a} + 7\sqrt a – 2\sqrt {2a} \\
= 10\sqrt a – 6\sqrt {2a} \\
d,\\
2\sqrt 3 + \sqrt {{{\left( {\sqrt 3 – 2} \right)}^2}} \\
= 2\sqrt 3 + \left| {\sqrt 3 – 2} \right|\\
= 2\sqrt 3 + \left( {2 – \sqrt 3 } \right)\\
= 2 + \sqrt 3
\end{array}\)