The equation of free vibrations of a system is $$\frac{{{{\text{d}}^2}{\text{x}}}}{{{\text{d}}{{\text{t}}^2}}} + 36{\pi ^2}{\text{x}} = 0{\text{,}}$$    its natural frequency is

A. μ₁ = μsinβ B. μ₁ = μcosβ C. $${\mu _1} = \frac{\mu }{{\sin \beta }}$$ D. $${\mu _1} = \frac{\mu }{{\cos \beta }}$$

A. Self-closed B. Force-closed C. Friction closed D. None of these

A. Sliding B. Turning C. Rolling D. Screw

A. None of the links is fixed B. One of the links is fixed C. Two of the links are fixed D. None of these