The function $f\left(x\right)=2\cos 5x+3\sin \sqrt{5}x$ is

Let $f\left(x\right)=\sin x+\cos ax$ be a periodic function. Then,

The function $f\left(x\right)=\left|sin4x\right|+\left|cos2x\right|,$ is a periodic function with a fundamental period 

Let $f:R\to R$ be a periodic function such that $f\left(T+x\right)=1+{\left[1-3f\left(x\right)+3{\left(f\left(x\right)\right)}^2-{\left(f\left(x\right)\right)}^3\right]}^{\frac{1}{3}}$, where $T$ is a fixed positive number, then period of $f\left(x\right)$ is