alleryIf a line makes angles $90^\circ, 60^\circ, 30^\circ$ with the x, y, z axes, the sum of squares of its direction cosines is:
A$\tfrac32$
B$0$
C1
D$2$
Answer & Solution
Correct answer: C. 1
Direction cosines are cos90°, cos60°, cos30° = 0, ½, √3/2; their squares sum to 0+¼+¾ = 1.
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