# Where did this equation come from?

I was perusing the internet and I came across a formula for the area of triangle in a coordinate plane.

With Vertices of (x1,y1) (x2,y2) (x3,y3)
Area= 1/2 [(y2-y1)(x1-x3)-(x2-x1)(y1-y3)]

There was no description with the formula. Where did it come from and why does it work?

## Answers and Replies

I was perusing the internet and I came across a formula for the area of triangle in a coordinate plane.

With Vertices of (x1,y1) (x2,y2) (x3,y3)
Area= 1/2 [(y2-y1)(x1-x3)-(x2-x1)(y1-y3)]

There was no description with the formula. Where did it come from and why does it work?

Look here http://en.wikipedia.org/wiki/Triangle#Using_Heron.27s_formula , under "using coordinates", the third "T" there.

DonAntonio