Toán 10

L

lp_qt

$\left\{\begin{matrix}tanx-cotx=1 & \\ tanx.cotx=1 & \end{matrix}\right. \Longleftrightarrow \left\{\begin{matrix} tanx=\dfrac{1+\sqrt{5}}{2} & \\ cotx=\dfrac{-1+\sqrt{5}}{2} & \end{matrix}\right.$

$t=tanx$

$\sin2x=\dfrac{2t}{1+t^2};\cos2x=\dfrac{1-t^2}{1+t^2}$
 
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