Please help to find #(sin phi)/2 if cos phi =-5/13#?

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1 Answer
maganbhai P.
Mar 6, 2018

#C:sqrt(9/13)#

Explanation:

#90^0 < phi < 180^0 rArr# second quadrant,#rArrsinphi>0#
#cosphi=-5/13. and45^0<(phi/2)<90^0#.
So, #sin(phi/2)=+sqrt((1-cosphi)/2)=sqrt((1+5/13)/2)=sqrt((13+5)/(2*13))=sqrt((18)/(2*13))=sqrt(9/13)#

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