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Vectors
Manjot Pahwa
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18 Mar 2008 11:10:56 IST
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using vectors prove that
sin(a+b)= sina*cosb + cosa*sinb


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sandeep ramesh's Avatar

sandeep ramesh
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18 Mar 2008 11:14:35 IST
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hint:
consider a unit circle and projections of a vector from its origin
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layman
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19 Mar 2008 15:04:02 IST
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Let the two vectors be a and b on a unit circle.
a=cos A i + sin A j
b=cos B i + sin B j
|axb|=sin A.cos B+cos A.sin B = |a|.|b|.sin(A+B)
=>sin(A+B) = sin A.cos B+cos A.sin B
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arpan1
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19 Mar 2008 15:06:57 IST
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someone pls post this type of related ques,...

i need them badly
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layman
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19 Mar 2008 15:07:42 IST
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Try proving cos(A-B)=cos A.cos B+sin A.sin B
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layman
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19 Mar 2008 15:07:59 IST
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Similar type only
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arpan1
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19 Mar 2008 15:17:57 IST
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pls post some more
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kaushik krishna
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19 Mar 2008 15:29:51 IST
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in that case a and b must b in the same quadrant with A>B
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arpan1
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19 Mar 2008 15:33:29 IST
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hey someone post more ques. of this type

multiple rates assured
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layman
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19 Mar 2008 15:45:07 IST
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1.Prove angle in a semicircle is 90.
2.Prove that in a rhombus diagonals bisect each other at right angles.
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ram kumar
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19 Mar 2008 16:12:59 IST
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here are my questions:::
 
1 . prove sine rule using vectors
 
\frac{a}{sinA}=\frac{b}{sinB}=\frac{c}{sinC}
 
2 . prove  using vectors    cosA=\frac{b^2+c^2-a^2}{2bc}
 
3. THIS IS A REALLY GOOD SUM
 
  prove Hero's formula using vectors
 
   Area= \sqrt{s(s-a)(s-b)(s-c)}
 
where a,b,c are sides of the triangle.......
 
 
 
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layman
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19 Mar 2008 16:14:19 IST
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I started a new thread for this
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