μ=tanθc\mu=\tan \theta_{c}μ=tanθc
μ=sinθc\mu=\sin \theta_{c}μ=sinθc
μ=1sinθc\mu=\dfrac{1}{\sin \theta_{c}}μ=sinθc1
μ=cosθc\mu=\cos \theta_{c}μ=cosθc