Question

if cos(x+y), cosx, cos(x+y) are in H.P. Find the value of cosx . sec y/x​

Answer 1

Answer:

Since cos(x−y),cosx,cos(x+y) are in H.P

We have

cosx=cos(x−y)+cos(x+y)2cos(x−y)cos(x+y)=2cosxcosy2(cos2x−sin2y)

⇒cos2xcosy=cos2x−sin2y⇒(1−cosy)cos2x=sin2y

⇒cos2x=1−cosysin2y=2sin2(2y)4sin2(2y)cos2(2y)

⇒cos2x=2cos2(2y)⇒cosxsec

Step-by-step explanation:

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