a.) Given polygon P with vertices (1,5), (4,8), (8,5), (6,2) and (2,1), find the following:
Find the area of P.
Tip: Make sure to move COUNTERCLOCKWISE from point to point to ensure you get a positive area.
b.) Find the vertices P' after reflection P over the x-axis.
Thanks for all the help
1) well there's a nice formula for the area of a triangle with vertices $(A_1, A_2), (B_1,B_2)$ and $(C_1, C_2)$:
$Area = (1/2) det\begin{pmatrix} B_1 - A_1 & C_1 - A_1 \\ B_2 - A_2 & C_2 - A_2 \end{pmatrix}$
and you can always split your polygon in a bunch of triangles
2) reflecting over x-axis just makes all y-coordinates change sign