1. The problem statement, all variables and given/known data In the notes , refer to the circled part . It 's stated that the shearing strain is positive when the angle formed by two surfaces oriented along positive y and x axes decreases .. 2. Relevant equations 3. The attempt at a solution . As we can see from the figure( paralleogram ) , one of the angle increases , while another angle decreases , am i right ? Why the author said angle decreases ?