Answer each of the following questions in one word or one sentence or as per exact requirement of the question:
Write the value of 
.
Given cos-1 (tan 3π/4)
= cos-1 (tan (π - π/4))
We know that tan (π – θ) = - tan θ
= cos-1 (-tan π/4)
= cos-1 (-1)
We know that cos-1 x = π
∴ cos-1 (tan 3π/4) = π
1