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1. Vectors question - area of quadrilateral
I have a question that I cant seem to find the answer to, im wondering if ayone can spot where im going wrong.

Given points A(1,0,10) B(7,4,0) C(-3,14,0) D(-9,4,16) which are coplanar, calculate the area of the quadrilateral ABCD

The way ive done it is finding AB and AC then using the cross product rule (matrix) to multiply these two together I get my answer as 89 units. But the answer im given on my sheet is 199.
Last edited by Diggedy; 13-05-2012 at 11:23. Reason: corrected typo
2. Re: Vectors question - area of quadrilateral
You have yet to consider point D. Peace.
3. Re: Vectors question - area of quadrilateral
I assumed it to be a parallelogram.
4. Re: Vectors question - area of quadrilateral
You can't do that, the quadrilateral doesn't necessarily have to be a parallelogram. Peace.
Last edited by WhiteGroupMaths; 13-05-2012 at 08:24.
5. Re: Vectors question - area of quadrilateral
so what do I do. Find vector CD and then use a 3x3 matrix?
6. Re: Vectors question - area of quadrilateral
(Original post by Diggedy)
I have a question that I cant seem to find the answer to, im wondering if ayone can spot where im going wrong.

Given points A(1,0,10) B(7,4,0) C(-3,14,0) D(-94,16) which are coplanar, calculate the area of the quadrilateral ABCD

The way ive done it is finding AB and AC then using the cross product rule (matrix) to multiply these two together I get my answer as 89 units. But the answer im given on my sheet is 199.

A, B and C each have three components. So why have you only got two components for D ?
7. Re: Vectors question - area of quadrilateral
typo! edited
8. Re: Vectors question - area of quadrilateral
(Original post by Diggedy)
typo! edited
Split your quadrilateral into two triangles, and work out the area of each. Quick sketch projecting onto the z=0 plane would be useful just to confirm the shape is convex.