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Find cos(u/2) if sin u = -0.085 and u is in Quadrant-IV. cos(u/2) =

 May 16, 2015

Best Answer 

 #1
avatar+128079 
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cosu = √[1 - (-.085)^2]  = about .99638

 

cos(u/2)  = ±√[(1 + cosu) / 2 ] = ±√[(1 + .99638) / 2] = about   ± 0. 999

 

But, if u lies in Q4, then u/2 lies in Q2.....and the cos is negative in that quadrant.....so

 

cos(u/2)  ≈ -0.999

 

 

 May 16, 2015
 #1
avatar+128079 
+5
Best Answer

cosu = √[1 - (-.085)^2]  = about .99638

 

cos(u/2)  = ±√[(1 + cosu) / 2 ] = ±√[(1 + .99638) / 2] = about   ± 0. 999

 

But, if u lies in Q4, then u/2 lies in Q2.....and the cos is negative in that quadrant.....so

 

cos(u/2)  ≈ -0.999

 

 

CPhill May 16, 2015

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