Calculating the Area of a Parallelogram with Given Vertices

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    Area Parallelogram
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Discussion Overview

The discussion revolves around calculating the area of a parallelogram defined by four vertices in a two-dimensional space. Participants explore various methods to approach the problem, including vector calculations and geometric interpretations.

Discussion Character

  • Exploratory, Technical explanation, Mathematical reasoning

Main Points Raised

  • One participant suggests using the cross product by adding a third coordinate of 0 to the vertices, as the cross product is not defined in R2.
  • Another participant proposes verifying the suggested method by attempting it to see if it yields the correct area.
  • A different approach involves calculating the base's magnitude and finding the height by determining an orthogonal vector from a vertex to the opposite side, then measuring the intersection point.
  • Another method mentioned includes using the inner product of adjacent vectors and the magnitudes of those vectors to find the area.

Areas of Agreement / Disagreement

Participants present multiple competing methods for calculating the area, with no consensus on which approach is superior or if any method is definitively correct.

Contextual Notes

Some methods depend on specific geometric interpretations and assumptions about the vectors involved, which may not be universally applicable without further clarification.

samazing18
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i'm posting this problem in the calculus forum because i got this question in a calculus class. It seems like a straightforward area problem, but i don't think that's the case and i can't figure out another way to do the problem using vectors.

"Find the area of the parallelogram with vertices (1,2), (4, 5), (5, 9), and (8, 12)."

any ideas?
 
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Add in a third coordinate of 0 and then find the magnitude of the cross product of two adjacent sides, since the cross product isn't defined in R2.
 
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If you know the answer already, try that out and see if it works.
 


Another way I thought of that doesn't involve the cross product would be to find the magnitude of the vector forming the base. Then find the magnitude of a vector that would be the height of the parallelogram. To do this, take one of the top vertices, and find a vector that is orthogonal to it and find the point at which that vector (the orthogonal one) intersects the other vector. Take the magnitude of the vector from that point of intersection to the original vertice and you should have the height. Then the area of the parallelogram is just base times height.
 


another, and perhaps simpler, ways is to take the difference of the inner product of adjacent vectors and multiplication of magnitudes of the adjacent vectors
 
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