remember that perimeter is the sum of the lengths of the sides. The way to find the length of the sides is [tex] \sqrt{ ( x_{2} - x_{1} )^{2} * ( y_{2} - y_{1} )^{2} }[/tex] where [tex] (x_{1},y_{1}) [/tex] is one endpoint of one line, while [tex] (x_{2},y_{2}) [/tex] is the other endpoint of the same line. Repeat this formula for each side and add them all together to get your perimeter
