Answers:
Perimeter = 58.5 centimeters
Area = 163.15 square centimeters
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Explanations:
To get the perimeter, you add up the three exterior (aka outer) sides. So you add up everything but the length measuring 13 cm, as this segment is not on the outside of the triangle. Imagine this is a parking lot and you want to put fencing around the outer sides. You won't build any fencing to run through the middle of the lot (assuming you don't want to subdivide)
So we add up 15.4, 18 and 25.1 to get 15.4+18+25.1 = 58.5 centimeters. The units stay at centimeters. We don't go to "square centimeters" like we do with the area below.
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To get the area of the largest triangle, we multiply the base and height, then divide by 2. The base is always perpendicular to the height
base = 25.1
height = 13
area = base*height/2 = 25.1*13/2 = 163.15 square cm
You write "square" before the "cm" to indicate the proper units for the area. Think of a 1 cm by 1 cm rectangle which has area of 1*1 = 1 square cm. This idea applies to triangles as well because we can subdivide the triangle into smaller squares, or you can move one piece of a triangle to another side to reshape the figure into a rectangle.
