Trigonometric graph analysis - point determination

Question

I don't fully understand this question as an explanation and example weren't given to it in the book.

I'm fluent in the material itself just don't understand its application in this sense

could you help explain it to me?

Thank You,

Answer 1

Hint, as you have not displayed much effort to solve.

Draw horizontal line segments (parallel to the x-axis) at say point 'a'.

Note, such a segment intersects the right part of the cosine curve just prior to the x-axis point of ${2\pi}$.

Per the provided information contained in the question, it is an x point apparently close to ${2\pi}$.

Which one based on symmetry?

Answer 2

Hint:

The query can be solved by exploring this.