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### Question Asked by a Student from EXXAMM.com Team

** Q 1830112012. ** If a variable line in two adjacent positions has direction cosines `I, m, n` and `l + delta l, m + delta m, n + delta n`, then show that the small angle `delta theta` between the two positions is given by `delta theta^2 = delta l^2 + delta m2 + delta n^2`