# The principal solution of cos-1(-1/2) is - Mathematics and Statistics

MCQ

The principal solution of cos^-1(-1/2) is :

#### Options

• pi/3

• pi/6

• (2pi)/3

• (3pi)/2

#### Solution

The principal solution of cos^-1(-1/2)=  An angle in [0,π], whose cosine is -1/2

⇒ cos^-1(-1/2) = pi - "cos"^-1 (1/2)   .....[because cos-1 (-x) = π - cos x]

= pi - pi/3 = (2pi)/3

Concept: Inverse Trigonometric Functions - Inverse Trigonometric Functions - Principal Value Branch
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