Question

If 310 = r, then the value of cos O cos 20 cos 40 cos 80 cos 160 is

1​

Answer 1

cos 40 + cos 80 + cos 160 + cos 240

= (40+80) cos( 2cos( 2 2 80)+cos(180-20) + cos(180 +

60)

40-80

= 2cos60.cos(-20) + (-cos20) + (-cos60)

cos C+cosD=2cos( C+D 2 ).cos( C-D 2 )

cos(180 + theta) = - cos theta cos(180 - theta) = - cos theta

= 2 x / cos (20) - cos(20) - -/ (cos(-0) = cose)

Feedback

COSAD+ (0550 + (at 160+ 6 zice

2105 60. (TO) + (-10520) + (-60)

cos20 cos20 - -1/2 = -½