Evaluate the trigonometric function using its period as an aid.
Cos 8π

A)cos 8π = -8
B)cos 8π = 0
C)cos 8π = 8
D)cos 8π = ∞
E)cos 8π = 1

Question

Evaluate the trigonometric function using its period as an aid. ​
Cos 8π
​
A)cos 8π = -8
B)cos 8π = 0
C)cos 8π = 8
D)cos 8π = ∞
E)cos 8π = 1

Quizplus · Accepted Answer

The cosine function has a period of 2π, meaning that cos(x + 2π) = cos x for any value of x. Therefore, we can write cos 8π = cos (4π + 4π) = cos 4π = 1, since the cosine function has a value of 1 at every multiple of 2π. Therefore, the best choice is E, cos 8π = 1.

Evaluate the Trigonometric Function Using Its Period as an Aid