$1, \mathrm{~m}, \mathrm{n}$, are the direction cosines of a straight line them (A) $l^{2}+m^{2}-n^{2}=1$ (B) $l^{2}-m^{2}+n^{2}=1$ (C) $l^{2}-m^{2}-n^{2}-1$ (D) $l^{2}+m^{2}+n^{2}=1$ - Noon Academy

$1, \mathrm{~m}, \mathrm{n}$ , are the direction cosines of a straight line them (A) $l^{2}+m^{2}-n^{2}=1$ (B) $l^{2}-m^{2}+n^{2}=1$ (C) $l^{2}-m^{2}-n^{2}-1$ (D) $l^{2}+m^{2}+n^{2}=1$

Maths | Previous Year Question Papers

$1, \mathrm{~m}, \mathrm{n}$ , are the direction cosines of a straight line them (A) $l^{2}+m^{2}-n^{2}=1$ (B) $l^{2}-m^{2}+n^{2}=1$ (C) $l^{2}-m^{2}-n^{2}-1$ (D) $l^{2}+m^{2}+n^{2}=1$

Correct option is (D) $l^{2}+m^{2}+n^{2}=1$

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