I keep getting “Direction ratios” questions wrong in Vectors & 3D Geometry. What's the trap?
confusing direction ratios with direction cosines (which are normalised).
The usual trap: confusing direction ratios with direction cosines (which are normalised). How to avoid it: direction cosines are direction ratios divided by the magnitude. Go back to the definition — the components that fix a line's or vector's direction in 3D space.
Key point
Direction ratios
Common mistake
confusing direction ratios with direction cosines (which are normalised).
Memory tip
direction cosines are direction ratios divided by the magnitude.
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