Answer:
34.79 (length units)
Step-by-step explanation:
To calculate the perimeter, we need to add up all the sides.
We use Pythagoras Theorem to calculate the side, taking the differences of the coordinates of the vertices, squaring and taking square-root.
Side 1: between (-9, -1) and (-1,-1)
Differences in coordinates: 8,0 => length = 8
side 2: between (-1,-1), (6,5)
differences in coordinates: 7,8, => length = sqrt(7^2+8^2) = sqrt(113)
side 3: between (6,5), (-9,-1)
differences in coordinates: 15,6 => length = sqrt(15^2+6^2) = 3sqrt(29)
Perimeter
= 8 + sqrt(113) + 3sqrt(29)
= 8 + 10.63 + 16.16
= 34.7856
