To find perimeter you must add all the side lengths together:
P = AB + BC + AC
The side lengths AC and BC are easy to find. You must simply count how many units they span. Please refer to the image below to see how I did this.
To find the length of AB is a bit trickier. Since the trianlge shown is a right trianlge you may use pythagorean theorem
[tex]a^{2} +b^{2}=c^{2}[/tex]
a and b are the legs (the sides that form a perpendicular/right angle)
c is the hypotenuse (the side opposite the right angle)
In this case...
a = 6
b = 7
^^^Plug these numbers into the theorem
[tex]6^{2} + 7^{2} = c^{2}[/tex]
solve for c
36 + 49 = [tex]c^{2}[/tex]
[tex]c^{2}[/tex] = 85
c ≈ 9.219
c ≈ 9.2 units
Hope this helped! Let me know if you have any further questions!
~Just a girl in love with Shawn Mendes
