Question

Determine o valor de N em:
N= cos 20° . cos 40° . cos 80°

Answer 1

cos 20° . cos 40° . cos 80° =

(2sen20º.cos 20° . cos 40° . cos 80°)/2sen20=

(sen40º.cos40.cos80)/2sen20

(2sen40º.cos40.cos80)/2.2sen20

(sen80.cos80)/4sen20

(2sen80.cos80)/2.4sen20

(sen160)/8sen20, como sen160=sen20, podemos cancelar sen160 com sen20 e escrever 1/8

resposta N = 1/8