Tính tổng

[yukitox100]

[Only registered and activated users can see links] 0cos2%5Calpha%20+C_n%5E2%20cos3%5Calpha%20+....+C_ n%5E%7Bn-1%7D%20cos%7Bn%5Calpha%7D+C_n%5En%20cos%5B%28n+1%2 9%5Calpha%5D

[Only registered and activated users can see links] 0sin2%5Calpha%20+C_n%5E2%20sin3%5Calpha%20+....+C_ n%5E%7Bn-1%7D%20sin%7Bn%5Calpha%7D+C_n%5En%20sin%5B%28n+1%2 9%5Calpha%5D

theo CT nhị thức Newton có:
[Only registered and activated users can see links] +.........+C%5En_n.x%5E%7Bn+1%7D%20%20%281%29
nhận thấy với [Only registered and activated users can see links] 0---%3Ex%5En=cos%20n.%5Calpha+i.sin%20n.%5Calpha
[Only registered and activated users can see links] 20%5Calpha%29.%281+cos%5Calpha%20+i.sin%5Calpha%29 %5En[Only registered and activated users can see links] alpha%29+C%5E1_n%28cos%5Calpha%20+i.sin%20%5Calpha %29%5E2+.........+C%5En_n.%28cos%5Calpha%20+i.sin% 20%5Calpha%29%5E%7Bn+1%7D[Only registered and activated users can see links] alpha%29+C%5E1_n%28cos2%5Calpha%20+i.sin%202%5Calp ha%29+.........+C%5En_n.%28cos%28n+1%29%5Calpha%20 +i.sin%28n+1%29%20%5Calpha%29[Only registered and activated users can see links] 2%5Calpha%20+............+C%5En_n.cos%28n+1%29%5Ca lpha%20%29+i.%28C%5Eo_n.sin%5Calpha%20+C%5E1_n.sin 2%5Calpha%20+............+C%5En_n.sin%28n+1%29%5Ca lpha%20%29

phân tích + cong thức Moivre có:
[Only registered and activated users can see links] ha%29.%281+cos%5Calpha%20+i.sin%5Calpha%29%5En=2%5 En.cos%5En%5Cfrac%7B%5Calpha%7D2.%5Bcos%7B%5Cfrac% 7Bn+2%7D2.%5Calpha+i.sin%7B%5Cfrac%7Bn.%5Calpha%7D 2%7D%5D( làm tắt chút hok gõ dược latex nữa >"<)

---->KQ
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