cosx+cosy+cosz=1+4sin(x/2)sin(y/2)sin(z/2)cosx+cosy=1-cosz+4sin(x/2)sin(y/2)sin(z/2)2cos[(x+y)/2]cos[(x-y)/2]=2sin^(z/2) -2sin(z/2)[cos[(x+y)/2]-cos[(x-y)/2][cos(x+y)/2 +sin(z/2)][cos(x+y)/2 -sin(z/2)...
已知x,y,z都是锐角,且cosx+cosy+cosz=1+4sinx/2×siny/2×sinz/2,求证:x+y+z
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