Answer :

Edufirst
Odd functions have the property that the average on the interval [-a,a] is zero, because of this:

The definition of the average of a differentiable function is:

Average = { ∫ f(x)dx from - a to a } / [ a - (-a)]

And for an odd fuction ∫f(x)dx from - a to a is zero => Average = 0

The only odd function in the list is cos(x), then the answer is b. cos(x).

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