[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(-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.

[WhiteGroupMaths]

You have yet to consider point D. Peace.

[Diggedy]

I assumed it to be a parallelogram.

[WhiteGroupMaths]

You can't do that, the quadrilateral doesn't necessarily have to be a parallelogram. Peace.

[Diggedy]

so what do I do. Find vector CD and then use a 3x3 matrix?

[steve2005]

(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 ?

[Diggedy]

typo! edited

[ghostwalker]

(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.