enter image description here

Normally my teacher would tell me to do $\vec{AB}$ x $\vec{AC}$ which have the same initial point and the cross product of that would be the line/vector perpendicular to the plane or perpendicular to those 2 vectors.

But in this question, we have different initial point. What does this mean and how can i visualise this? Does this have to do with: enter image description here ?


1 Answer 1


Vectors $\overrightarrow{AB}=B-A=(-1,-3,1)$ and $\overrightarrow{AC}=C-A=(0,-2,1)$ can be viewed as vectors starting at the origin therefore nothing change in the calculation for dot or cross product. In other words, in both cases we can consider $A$ as the origin for this purpose.

  • $\begingroup$ Sorry i think i might not have addressed my question properly, my question should have been the difference $\vec{AB}$ x $\vec{BC}$ and $\vec{AB}$ x $\vec{AC}$ $\endgroup$
    – CountDOOKU
    Commented Nov 4, 2019 at 23:03
  • $\begingroup$ @FredWeasley For all these vectors we can proceed as usual we always can assume the first point as the origin for that vector. $\endgroup$
    – user
    Commented Nov 5, 2019 at 6:04

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