The following state of strain is measured at a point on surface of crane hook's ${}_A=1000\frac{m}{m}($at $-15$ angle$),{}_B=-250\frac{m}{m}($at $30$ angle$),{}_C=200\frac{m}{m}($at $75$ angle$).$ Evaluate the values and orientation of the principal stresses at the point, Let $E=200$GPa and $v=0\mathrm{.}285.$

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