Maths · Inverse trigonometrical functions and their properties

If then find the value of

If \( \cos ^{-1} \lambda+\cos ^{-1} \mu+\cos ^{-1} \gamma=3 \pi \) then find the value of \( \lambda \mu+\mu \gamma+\gamma \lambda \)

  • A. 1
  • B. 2
  • C. 3 \)
  • D. 4

Step-by-step solution

The range of cos^{-1} is [0, π], so the maximum sum of three such angles is 3π, attained only when each angle equals π. Thus cos^{-1}(λ)=π, cos^{-1}(μ)=π, cos^{-1}(γ)=π, giving λ=μ=γ=-1. Then λμ+μγ+γλ = (-1)(-1)+(-1)(-1)+(-1)(-1)=1+1+1=3.
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