Consider the line . Then which of the following is/are true?
(A) It has Direction ratios (2, -3, -1)
(B) It has Direction cosines
(C) It has Direction ratios
(D) It has Direction cosines
Choose the correct answer from the options given below:
Consider the line . Then which of the following is/are true?
(A) It has Direction ratios (2, -3, -1)
(B) It has Direction cosines
(C) It has Direction ratios
(D) It has Direction cosines
Choose the correct answer from the options given below:
Solution
The line is given as
The standard form of a line in 3D is where are the direction ratios.
The y-term can be rewritten:
Since is constant, the line doesn't move in the z-direction. This is written as:
When a coordinate is constant, its direction ratio is 0.
The line in standard form:
Direction Ratios
Direction cosines are normalized direction ratios:
For :
Direction cosines:
(A) Direction ratios - Incorrect. The z-direction ratio is 0, not -1, and y-direction ratio is , not -3.
(B) Direction cosines - Incorrect. The z-direction cosine is 0, not .
(C) Direction ratios - Correct.
(D) Direction cosines - Correct.
Therefore, options (C) and (D) are true.
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