The state of stress at a point is given by:
\[ \sigma_{x}=60 M P a, \sigma_{\mathrm{y}}=-30 M P a, \tau_{\mathrm{xy}}=30 M p a(c c w) \]
Calculate

(a) principal stresses,

(b) principal planes,

(c) maximum shear stress, shown the orientation of principal planes and planes of maximum shear stress. Use Mohr's circle.