Show that cos 24 + cos 55 + cos 125 + cos 204 + cos 300= 1/2

(cos24+cos204)+(cos55 + cos125) +cos300 = 1/2

L.H.S.

= (2cos112cos90) + (2cos90cos35) + cos(360-60)

= (2cos112.0) + (2cos35.0) +cos60......[ bcoz cosx + cosy = 2cos(x+y)/2cos(x-y)/2 ] and [cos90 = 0]

= 0 + 0 + 1/2

= 1/2 

= R.H.S.

hence prOved

  • 9

L.H.S. = cos24+cos204+cos55 + cos125 +cos300

= cos 24 + cos (180+24) + sin (90-55) + cos (90+35) + cos (360-60)  [ cos x = sin (90-x)]

= cos 24 - cos 24 + sin 35 - sin 35 + cos 60  [ cos (180 + x ) = - cosx  ;   cos (90 + y ) = - sin y ; cos (360 - x ) = cos x  ]

= (cos 24 - cos 24) + (sin 35 - sin 35 )+ cos 60

= 0 + 0 + 1/2 = 1/2 = R.H.S.

  • 62
Cos10
  • -15
sh
  • -10
your question is wrong
all these trignometric ratios should be in addition not in multiplication.....
  • -6
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