alleryStart learning →True or false: direction cosines
Exercise and reference answers
- Questions
- Statement is true
- Yes
- Statement
- For any line, l² + m² + n² = 1.
- Statement is true
- No
- Statement
- Direction ratios must also satisfy a² + b² + c² = 1.
- Statement is true
- Yes
- Statement
- Direction cosines are the cosines of the angles made with the axes.
- Statement is true
- No
- Statement
- A line has exactly one set of direction ratios.
- Statement is true
- Yes
- Statement
- Direction ratios are proportional to the direction cosines.
Explanation
Direction cosines are normalised, direction ratios are not.
That single difference decides most questions here.
Source: syllabus Maths Part II, Ch 11 Three Dimensional Geometry.
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