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Noody hasn't added any friends yet.
19-08-2008 - 14:43
25-12-2007 - 21:29
Cho x,y,z là ba góc bất kì thoả mãn :hệ sinx+siny+sinz=0 và cosx+cosy+cosz=0chứng minh rằng: 1,sin2x +sin2y +sin2z=0 2sin(x+y+z)=\dfrac{1}{3}(sin3x+sin3y+sin3z) 3,cos(x+y+z)=\dfrac{1}{3}(cos3x+cos3y+cos3z)Trả lời sớm hộ mình