If $\sigma_1$ and $\sigma_3$ are the algebraically largest and smallest principal stresses respectively, the value of the maximum shear stress is
- $\dfrac{\sigma_1 +\sigma_3}{2} \\$
- $\dfrac{\sigma_1 -\sigma_3}{2} \\ $
- $\sqrt{\dfrac{\sigma_1 +\sigma_3}{2}} \\$
- $\sqrt{\dfrac{\sigma_1 -\sigma_3}{2}}$