Rút gọn: C = (Sin(x+y)) / ( Sin x + Sin y ) 19/10/2021 Bởi Charlie Rút gọn: C = (Sin(x+y)) / ( Sin x + Sin y )
Ta có $C = \dfrac{\sin(x+y)}{\sin x + \sin y}$ $= \dfrac{2\sin\left( \frac{x + y}{2} \right) \cos \left( \frac{x + y}{2} \right)}{2 \sin \left( \frac{x + y}{2} \right) \cos \left( \frac{x-y}{2} \right)}$ $= \dfrac{\cos \left( \frac{x + y}{2} \right)}{\cos \left( \frac{x-y}{2} \right)}$ Vậy $C= \dfrac{\cos \left( \frac{x + y}{2} \right)}{\cos \left( \frac{x-y}{2} \right)}$ Bình luận
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Ta có
$C = \dfrac{\sin(x+y)}{\sin x + \sin y}$
$= \dfrac{2\sin\left( \frac{x + y}{2} \right) \cos \left( \frac{x + y}{2} \right)}{2 \sin \left( \frac{x + y}{2} \right) \cos \left( \frac{x-y}{2} \right)}$
$= \dfrac{\cos \left( \frac{x + y}{2} \right)}{\cos \left( \frac{x-y}{2} \right)}$
Vậy
$C= \dfrac{\cos \left( \frac{x + y}{2} \right)}{\cos \left( \frac{x-y}{2} \right)}$