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A point in a body under plane stress conditions has a state of stress given by non-zero sigma_(xx) and sigma_(vy) but with tau_(xy)-0. The material constants are E and nu. A strain gauge placed at the point is orientated in such a way that its reading of the normal strain (along its own axis) is dependent only on sigma_(yy) but not on sigma_(xx). Show that the orientation theta is given by tan theta=(1)/(sqrtnu).