all graphs are -2π,2π by -2,2. is f(x)=1.4(cos x)^2 periodic? no yes

Explanation:

Step1: Recall cosine - function property

The cosine function (y = \cos x) is periodic with period (T = 2\pi), i.e., (\cos(x + 2\pi)=\cos x) for all (x\in R).

Step2: Analyze the given function

Let (f(x)=1.4(\cos x)^{2}). Then (f(x + 2\pi)=1.4(\cos(x + 2\pi))^{2}). Since (\cos(x + 2\pi)=\cos x), we have (f(x + 2\pi)=1.4(\cos x)^{2}=f(x)).

Answer:

Yes