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2 tan^-1(tan x/2 tan y/2)= cos^-1( cos x + cos y / 1+ cos x cos y)

2 tan^-1(tan x/2 tan y/2)= cos^-1( cos x + cos y / 1+ cos x cos y)

Grade:12

1 Answers

Arun
25750 Points
6 years ago
Dear student
 

We have,

sinA + sin2A = 1   ...(1) 

⇒ sinA = – sin2A   ...(2)

Now

cos2+ cos4

= (– sin2A) + {(1 – sin2A)}2

= sinA + sin2[from (2)]  

= 1 [from (1)]

 

Regards

Arun (askIITians forum expert)

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