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Co - ordinate Geometry 3D Geometry

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The projection of a line on the axes are 2, 3, 6 then the length of line is

A. 5

B. 2√5

C. 7

D. Cannot determine

E. None of the above

View Answer

Correct choice: C

Explanation:

Let the length of the line is r and direction cosine of the line are l, m, n
∴ r cosα = 2 = rl; rcosβ = 3 = rm; rcosγ = 6 = rm
∴ (rl)² + (rm)² + (m)² = 2² + 3² + 6²
Or r² (l² + m² + n²) = 49
∴ r = 7

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Eamcet Mathematics Co - ordinate Geometry 3D Geometry

Eamcet Mathematics
Co - ordinate Geometry 3D Geometry