Question

Determine the sign of cos pi divided by three without using a calculator.

Answer 1

positive

Explanation:

To solve this, we can look at the unit circle (see attached photo), We know:

(0,1) = π/2

(-1, 0) = π

(0, -1) = 3π/2

(1, 0) = 0

Across the circle, we know that π/3 is between 0 and π/2. Therefore, as the unit circle line between that is positive in the x direction (cos), we can say that cos(π/3) is positive