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![[Post New]](/templates/default/images/icon_minipost_new.gif) 18 Jun 2007 17:22:55 IST
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Find the value of: cos 12 + cos 84 + cos156 + cos 288. (The angles are in degrees.)
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18 Jun 2007 17:40:20 IST
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is it 0.478 ????????
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the value is -1/2
as we know that
cos(a) + cos( a+d) + cos( a+2d)......=[sin(nd/2)/sin(d/2)][ cos(2a+(n-1)d]
by putting values we get
sin144/sin36 * cos120 = -1/2
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adversities cause some men to break other to break records............i m of the other type....... :-) |
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18 Jun 2007 18:50:06 IST
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rate if correct
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adversities cause some men to break other to break records............i m of the other type....... :-) |
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18 Jun 2007 19:18:43 IST
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another way is to multiply divide whole term by 2sin12
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adversities cause some men to break other to break records............i m of the other type....... :-) |
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19 Jun 2007 14:43:21 IST
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The answer is :
0.4
Rate me ..... :)
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Belive in the Best, Have a goal for your Best, Never be satisfied with less than your Best, And in the long run things will turn out for the Best. Always add up the Best.
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19 Jun 2007 18:37:22 IST
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u people i think are using calculator.May be not bbut prove ur answers
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adversities cause some men to break other to break records............i m of the other type....... :-) |
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19 Jun 2007 18:40:01 IST
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how did you get this?
cos(a) + cos( a+d) + cos( a+2d)......=[sin(nd/2)/sin(d/2)][ cos(2a+(n-1)d]
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19 Jun 2007 18:41:57 IST
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a fourmula though .other way when not using fourmula is also given multiply divide by 2sin12
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adversities cause some men to break other to break records............i m of the other type....... :-) |
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19 Jun 2007 18:42:36 IST
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if u haven't heard this ,then this is a useful fourmula.U can always learn new things!!!!!!1
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adversities cause some men to break other to break records............i m of the other type....... :-) |
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19 Jun 2007 18:51:04 IST
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can you prove it?
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