The Goal

Find the exact value of:

The Mistake

Find the mistake:

Need a hint? Look carefully at the red part:

The Correction

An Explanation

The angle 5π/6 lies in the second quadrant, with reference angle π - 5π/6 = π/6. Sine is positive in the second quadrant, and so sin(5π/6) = +sin(π/6) = 1/2.

You are expected to know the exact values of the trigonometric functions at all the nice angles. Visit Trigonometric Facts to help learn these values.