Simplificando se y= cos80°+cos40°-cos20°, obtém se...
A)0
B) Sen 20°
C)1
D)1/2
E) -1
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cos80°+cos40°-cos20°
2cos[(80+40)/2].cos[(80-40)/2] - cos20 =
2cos[(120)/2].cos[(40)/2] - cos20 =
2cos60.cos20 - cos20 =
2(1/2).cos20 - cos20 =
cos20 - cos20 = 0
2cos[(80+40)/2].cos[(80-40)/2] - cos20 =
2cos[(120)/2].cos[(40)/2] - cos20 =
2cos60.cos20 - cos20 =
2(1/2).cos20 - cos20 =
cos20 - cos20 = 0
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