Answer:
D.) cos(6π/5)
Explanation:
In a unit circle, cosine is defined as x-coordinate and sine is defined as y-coordinate.
This is because cosine is defined as x/r but since it’s a unit circle, r = 1 therefore, cosine = x,
Sine is defined as y/r but it’s a unit circle so sine = y.
Therefore, we ignore choices with sine.
Next, since this π/5 angle is in the third quadrant. π/5 is supposed to be in the first quadrant so to convert from first quadrant angle or reference angle to the third quadrant angle or opposite side, add the reference angle or π/5 by π.
Therefore, π/5 + π = π/5 + 5π/5
= 6π/5
Since we want to find x-coordinate which is cosine, therefore.
The answer is cos(6π/5)