Question 928179
p(6,4) Q(-3,1) and R(9,-5)

first draw a triangle:

{{{drawing(600,600,-10,10,-10,10,

circle(-3,1,.1),
circle(6,4,.1),
circle(9,-5,.1), 
line(-3,1,6,4),
   line(6,4,9,-5),
   line(9,-5,-3,1),
   locate(-3,1,Q(-3,1)), 
locate(6,4,p(6,4)), 
locate(8.2,-5,R(9,-5)),graph(600,600,-10,10,-10,10,0) 
 ))}}} 


to find perimeter, we need the length of sides, and the length of side is equal to distance between two points

so, we will find the distance between points p(6,4) and Q(-3,1), then Q(-3,1) and R(9,-5), and finally p(6,4) and R(9,-5)


a) the distance between points p(6,4) and Q(-3,1)


*[invoke hummingbird_distance_2D 6, 4, -3, 1]

so, the length of the side {{{pQ=9.5}}}


b) the distance between points  Q(-3,1) and R(9,-5)

*[invoke hummingbird_distance_2D 9, -5, -3, 1]


the length of the side {{{QR=13.4}}}


c) the distance between points p(6,4) and R(9,-5)

*[invoke hummingbird_distance_2D 9, -5, 6, 4]


the length of the side {{{pR=9.5}}}


then, perimeter {{{P=pQ+QR+pR}}}=>{{{P=9.5+13.4+9.5}}}=>{{{P=32.4}}}