jee-main 2021 Q77

jee-main · India · session1_25feb_shift1 Vectors: Lines & Planes Dihedral Angle or Angle Between Planes/Lines

Let $\alpha$ be the angle between the lines whose direction cosines satisfy the equations $l + m - n = 0$ and $l ^ { 2 } + m ^ { 2 } - n ^ { 2 } = 0$. Then the value of $\sin ^ { 4 } \alpha + \cos ^ { 4 } \alpha$ is :
(1) $\frac { 5 } { 8 }$
(2) $\frac { 1 } { 2 }$
(3) $\frac { 3 } { 8 }$
(4) $\frac { 3 } { 4 }$

Let $\alpha$ be the angle between the lines whose direction cosines satisfy the equations $l + m - n = 0$ and $l ^ { 2 } + m ^ { 2 } - n ^ { 2 } = 0$. Then the value of $\sin ^ { 4 } \alpha + \cos ^ { 4 } \alpha$ is :\\
(1) $\frac { 5 } { 8 }$\\
(2) $\frac { 1 } { 2 }$\\
(3) $\frac { 3 } { 8 }$\\
(4) $\frac { 3 } { 4 }$

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