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Order the steps: direction ratios to direction cosines

Exercise and reference answers

Steps
  1. Start from the direction ratios a, b, c
  2. Square each of them and add the three squares
  3. Take the square root of that sum
  4. Divide each of a, b and c by that root
  5. The results are the direction cosines l, m, n

Explanation

Your syllabus gives l = a/√(a²+b²+c²) and similarly for m and n, which is exactly this normalising procedure. Source: syllabus Maths Part II, Ch 11 Three Dimensional Geometry.
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