Toán Lớp 9: cho B =(1/ √x + 3 + 1/ √x -3 )* (1-3/ √)
rút gọn B và tìm x để B = 1/3
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Toán Lớp 9: cho B =(1/ √x + 3 + 1/ √x -3 )* (1-3/ √)
rút gọn B và tìm x để B = 1/3
Comments ( 1 )
Dkxd:x > 0;x\# 9\\
B = \left( {\dfrac{1}{{\sqrt x + 3}} + \dfrac{1}{{\sqrt x – 3}}} \right)\left( {1 – \dfrac{3}{{\sqrt x }}} \right)\\
= \dfrac{{\sqrt x – 3 + \sqrt x + 3}}{{\left( {\sqrt x + 3} \right)\left( {\sqrt x – 3} \right)}}.\dfrac{{\sqrt x – 3}}{{\sqrt x }}\\
= \dfrac{{2\sqrt x }}{{\sqrt x + 3}}.\dfrac{1}{{\sqrt x }}\\
= \dfrac{2}{{\sqrt x + 3}}
\end{array}$