SOLUTION: Find the area of a parallelogram with vertices (0, 0), (3, 3), (4, 6), and (7, 9) using the formula which relates the area to the absolute value of the determinant of the matrix.

Algebra ->  Matrices-and-determiminant -> SOLUTION: Find the area of a parallelogram with vertices (0, 0), (3, 3), (4, 6), and (7, 9) using the formula which relates the area to the absolute value of the determinant of the matrix.       Log On


   



Question 1071016: Find the area of a parallelogram with vertices (0, 0), (3, 3), (4, 6), and (7, 9) using the formula which relates the area to the absolute value of the determinant of the matrix.
What are the steps involved in solving this? I greatly appreciate any and all assistance. Thank you!

Found 2 solutions by Edwin McCravy, ikleyn:
Answer by Edwin McCravy(20054) About Me  (Show Source):
You can put this solution on YOUR website!

To find out what order to taken the vertices, we plot
the parallelogram:




To get the positive value of the area, take the coordinates 
going counter-clockwise around the polygon. Put the first
pair of coordinate (0,0) again at the bottom:



To evaluate that determinant, add all the NW to SE diagonal
products and subtract all the NE to SW diagonal products.

(0×3)+(3×9)+(7×6)+(4×0)-(0×3)-(3×7)-(9×4)-(6×0) =

  0  +  27 +  42 +   0 -   0 -  21 -  36 -   0  =

 12.  

Multiply by 1%2F2:

So 

Edwin

Answer by ikleyn(52776) About Me  (Show Source):
You can put this solution on YOUR website!
.
Let V1 = (a,b) and V2 = (c,d) be two vectors that are two adjacent sides of the parallelogram released from one common vertex. 


Then the area of the parallelogram is the absolute value of the determinant


S = abs (det %28matrix%282%2C2%2C+a%2Cb%2C+c%2Cd%29%29 ) = | ad - bc |.


In your case, it is convenient to take point (0,0) as the common vertex.

Then two vectors/adjacent sides are 

V1 = (3-0,3-0) = (3,3),     (1)    and

V2 = (4-0,6-0) = (4,6).     (2)

Do not mix these vectors (1) and (2) with the point coordinates.  
Again, (1) and (2) represent the vectors that are two adjacent sides of the parallelogram with the common vertex (0,0).

Next, form this matrix  %28matrix%282%2C2%2C+a%2Cb%2C+c%2Cd%29%29 = %28matrix%282%2C2%2C+3%2C3%2C+4%2C6%29%29.


Calculate its determinant  det = 3*6 - 4*3 = 18 - 12 = 6.


Take the absolute value of the determinant:  |det| = |6| = 6.


In this case the absolute value is the same as the determinant, but in other cases it may not be so.


Your area is 6:  S = 6 square units.


So, I answered your question and described the procedure.

See the lesson
    - Determinant of a 2x2-matrix and the area of a parallelogram and a triangle.
in this site.


Also, you have this free of charge online textbook in ALGEBRA-II in this site
    - ALGEBRA-II - YOUR ONLINE TEXTBOOK.

The referred lesson is the part of this online textbook under the topic
     "2x2-Matrices, determinants, Cramer's rule for systems in two unknowns"