RD Sharma - Mathematics (Volume 1)

Book: RD Sharma - Mathematics (Volume 1)

Chapter: 4. Inverse Trigonometric Functions

Subject: Maths - Class 12th

Q. No. 13 of Very short answer

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13

Answer each of the following questions in one word or one sentence or as per exact requirement of the question:

Write the value of cos–1(cos 1540°).


Given cos-1 (cos 1540°)


= cos-1{cos (1440° + 100°)}


= cos-1{cos (360° × 4 + 100°)}


We know that cos (2π + θ) = cos θ


= cos-1{cos 100°}


We know that cos-1 (cos θ) = θ if θ [0, π]


= 100°


cos-1 (cos 1540°) = 100°


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