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Topic overview

Long vector questions often stack intersection, perpendicularity, distance and positional constraints together. Every verbal condition should be converted into an independent equation.

Key concepts

Write the line as r=a+λd\mathbf r=\mathbf a+\lambda\mathbf d. For intersection, set the three coordinates equal; for perpendicularity, use zero dot product; the shortest vector from a point to a line is perpendicular to the direction vector.

Key points

  • ◆Do not mix up the parameters
  • ◆The three coordinate equations must be compatible
  • ◆Distance must be taken as the magnitude of the vector

Worked examples

Try each example yourself before checking the explanation.

1foot-of-perpendicular parameter

What is the parameter of the foot of the perpendicular from point PP to the line r=a+λd\mathbf r=\mathbf a+\lambda\mathbf d?

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