What is the principal value of ?

Answer and explanation

Correct answer: A.

Step 3. Since , subtract: .
  1. Step 1: The principal value branch for the inverse cosine function is .
  2. Step 2: Apply the inverse cosine reflection identity: .
Answer
.
Why not the others: is the inverse cosine of , falls outside the principal range , and lies in the third quadrant.

Practise more Basic results.

Free questions with an explanation for every one, and full timed AP (Advanced Placement) mock tests.