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Ex 11.1, 1 If a line makes angles 90°, 135°, 45° with the x, y and z – axes respectively, find its direction cosines. Direction cosines of a line making angle 𝛼 with x – axis, 𝛽 with y – axis and 𝛾 with z – axis are l, m, n l = cos 𝜶, m = cos 𝜷, n = cos 𝜸 Here, 𝛼 = 90°, 𝛽 = 135°, 𝛾 = 45°, So, direction cosines are l = cos 90° 𝒎 = cos 135° 𝒏 = cos 45° = 0 = cos (180 – 45°) = –cos 45° = (−𝟏)/√𝟐 = 𝟏/√𝟐 Therefore, required direction cosines are 0, ( −𝟏)/√𝟐 , 𝟏/√𝟐 .

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Davneet Singh

Davneet Singh has done his B.Tech from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths, Science, Social Science, Physics, Chemistry, Computer Science at Teachoo.