Book: RS Aggarwal - Mathematics
Chapter: 4. Inverse Trigonometric Functions
Subject: Maths - Class 12th
Q. No. 4 C of Exercise 4C
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4 C
Prove that:
To Prove: 
Formula Used:
1) cos 2A = 2 cos2 A – 1
2) 
Proof:
LHS 
= cos-1 (2x2 – 1)… (1)
Let x = cos A … (2)
Substituting (2) in (1),
LHS = cos-1 (2 cos2 A – 1)
= cos-1 (cos 2A)
= 2A
From (2), A = cos-1 x,
2A = 2 cos-1 x
= RHS
Therefore, LHS = RHS
Hence proved.
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