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(xi)cos 80° + cos 40º - cos 20º = 0 |
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Answer» cos80°+cos40°-cos20°=0 we know that; [cosx+cosy]=2COS(x+y)/2.cos(x-y) /2] so, cos80°+cos40°=2cos(80°+40°) /2.cos(80°-40°) /2 = 2cos60°(cos20°) -cos20° =cos20°(2.1/2-1) =cos20°(1-1) =cos20°(0) =0 |
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