Tính A=cos120°+3sin0° ______________ 3tan45°-7cot60°

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1. Ta có:

   `A={cos120°+3sin0°}/{3tan45°-7cot60°}`

   $A=\dfrac{\dfrac{-1}{ 2 }+ 3. 0 }{3 . 1- 7 . \dfrac{1}{\sqrt{3}}}$

   $A=\dfrac{\dfrac{-1}{2}}{\dfrac{3\sqrt{3}-7}{\sqrt{3}}}$

   $A=\dfrac{-\sqrt{3}}{2(3\sqrt{3}-7)}$

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2. + $A = cos120° + 3sin0°$

   $= -\frac{1}{2} + 3.0$ 

   $= – \frac {1}{2}$.

   + $B = 3tan45° – 7cot60°$

   $= 3.1 – 7.\frac{1}{\sqrt {3}}$

   $= 3 – \frac {7\sqrt {3}}{3}$

   $= \frac{9 – 7 \sqrt {3}}{3}$.

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