The perimeter of the triangle ABC is 12.9 units.
What is the perimeter of a triangle?
The perimeter of a triangle is the sum of length of three sides of the triangle.
Given, the triangle ABC is rotated by 135 degrees about point S to create the triangle A'B'C'.
We know, after rotation of a figure, the whole dimension of the figure remains the same.
Therefore, AB = A'B' = 5.1 units
BC = B'C' = 2 units
CA = C'A' = 5.8 units
Hence, the perimeter of the triangle ABC
= (5.1 + 2 + 5.8) units
= 12.9 units
Learn more about the perimeter of a triangle here: https://brainly.com/question/19219426
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