Friday, May 31, 2013

Using double angle formula find the exact value

, given secθ=4,3pi/2<θ<2pi 
sin2θ= 
cos2θ= 
tan2θ=


sec%28theta%29=4, 


cos%28theta%29=1%2F4 

3pi%2F2%3Ctheta%3C2pi 

i.e. we are in quadrant IV 

means... 

sin%28theta%29=-sqrt%2815%29%2F4 
 


cos2%2Atheta=2cos%5E2%28theta%29-1=2%281%2F4%29-1=-1%2F2 


We forgo using tangent identities since we don't need them 
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