Question
Thu July 14, 2011 By:

if sin(a + b)= 1, then cos(a - b) = ?

Expert Reply
Thu July 14, 2011
sin(a+b)=1
we can replace 1 by sin 90
=> sin(a+b)=sin(90)
=> a+b= 90
hence,cos(a+b)=0
now expanding
=> cosacosb-sinasinb=0
=> cosacosb=sinasinb
=> tana=tanb
hence angle a=b
=> a-b=0
therefore, cos(a-b)=1
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