Originally Posted by

**superdude** I am trying to calculate the area of a triangle given the points (3,3) (-1,-1) (4,1).

I am having trouble calculating the determinant

$\displaystyle

\left[\begin{matrix}

3 & 3 & 1\\

-1 & -1 & 1\\

4 & 1 & 1

\end{matrix} \right]

=-

\left[\begin{matrix}

-1 & -1 & 1\\

3 & 3 & 1\\

4 & 1 & 1

\end{matrix} \right]

=

\left[\begin{matrix}

1 & 1 & -1\\

3 & 3 & 1\\

4 & 1 & 1

\end{matrix} \right]

=

\left[\begin{matrix}

1 & 1 & -1\\

0 & 0 & 4\\

0 & -3 & 5

\end{matrix} \right]

$

since there is a 0 in the very middle of the last determinant, the product along the diagonal is 0. The answer key says I should get 6 but I can't find where I'm going wrong