RS Aggarwal - Mathematics

Book: RS Aggarwal - Mathematics

Chapter: 4. Inverse Trigonometric Functions

Subject: Maths - Class 12th

Q. No. 3 B of Exercise 4C

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3 B

Prove that:


To Prove: cos-1 (4x3 – 3x) = 3 cos-1 x


Formula Used: cos 3A = 4 cos3 A – 3 cos A


Proof:


LHS = cos-1 (4x3 – 3x) … (1)


Let x = cos A … (2)


Substituting (2) in (1),


LHS = cos-1 (4 cos3 A – 3 cos A)


= cos-1 (cos 3A)


= 3A


From (2), A = cos-1 x,


3A = 3 cos-1 x


= RHS


Therefore, LHS = RHS


Hence proved.


Chapter Exercises

Exercise 4A
Exercise 4B
Exercise 4C
Exercise 4D
Objective Questions

More Exercise Questions

1 A

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1 B

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2

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3 A

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3 C

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5 A

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5 B

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6 C

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6 F

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6 H

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7 A

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7 B

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7 C

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