Let coordinates of the triangle be defined as:
P(-4,-2)
Q(-3,-5)
R(3,-7)
Use distance formula between two points as
distance = sqrt((x2-x1)^2+(y2-y1)^2)
So
Dpq=sqrt((-3--4)^2+(-5--2)^2)=sqrt(1^2+3^2)=sqrt(10)=3.162
Dqr=sqrt((3--3)^2+(-7--5)^2)=sqrt(6^2+2^2)=sqrt(40)=6.325
Drp=sqrt((-4-3)^2+(-2--7)^2)=sqrt(7^2+5^2)=sqrt(74)=8.602
Add up the lengths of the three sides to get perimeter
= 3.162+6.325+8.602
= 18.089 units.
