Question 1037610
To get the Perimeter you need to get the distance between two points 
then add them

Perimeter of Triangle = a+b+c
a=AB
b=BC
c=AC
distance formula for two points 
{{{d =sqrt( (x2-x1)^2+(y2-y1)^2) }}} 

AB=sqrt((x2-x1)^2+(y2-y1)^2)
AB=sqrt((4--4)^2+(5--1)^2)
AB=sqrt(64+36)
AB=sqrt(100)
AB=10
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BC=sqrt((x2-x1)^2+(y2-y1)^2)
=sqrt((4-4)^2+(-2-5)^2)
=sqrt(0+49)
=sqrt(49)
=7
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AC=sqrt((x2-x1)^2+(y2-y1)^2)
=sqrt((4--4)^2+(-2--1)^2)
=sqrt(64+1)
=sqrt(65)
=8.06225774829855
=8.0623
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perimeter = 10+7+8.0623

P= 25.0623