Perimeter Composite Figures

Perimeter - How it Works - Video

Example 1

Example 1:

For composite figures, the first step is to find the missing side lengths. Once we identify the missing side lengths, in this case the red lines, we can start the process. One characteristic that we need to remember is that opposite sides of rectangles are the same. One of the side lengths that is missing is the 7 cm. We find that by using the 4 cm and the 11 cm because 4 cm + x = 11 cm. Remember that opposite sides are equal. So 11 is the total length of the figure, if we extend the smaller rectangle upward, then we get 4 cm + x = 11 cm, and x = 7 cm.

Now the other side length that is missing is the 3 cm. We find that by using 7 cm and 10 cm because x + 7 cm = 10 cm. Once again remember that opposite sides are equal. So 10 cm is the total length, and we extend the left rectangle to the right, then we get x + 7 cm = 10 cm, and x = 3 cm.

Remember perimeter is the length of all side lengths, that is why we found the missing side lengths. Now we add all 6 sides, 4 + 7 + 7 + 3 + 11 + 10 = 42 cm.

Example 2

Example 2:

For composite figures, the first step is to find the missing side lengths. Once we identify the missing side lengths, in this case the red lines, we can start the process. One characteristic that we need to remember is that opposite sides of rectangles are the same. One of the side lengths that is missing is the 4 cm. We find that by using the 3 cm and the 7 cm because x + 3 cm = 7 cm. Remember that opposite sides are equal. So 7 is the total length of the figure, if we extend the left rectangle to the right, then we get x + 4 cm = 7 cm, and x = 4 cm.

Now the other side length that is missing is the 8 cm. We find that by using 2 cm and 6 cm because 2 cm + 6 cm = x. Once again remember that opposite sides are equal. So x is the total length, and we extend the right rectangle upward, then we get 2 cm + 6 cm = x, and x = 10 cm.

Remember perimeter is the length of all side lengths, that is why we found the missing side lengths. Now we add all 6 sides, 2 + 4 + 6 + 3 + 8 + 7 = 30 cm.

Example 3

Example 3:

For composite figures, the first step is to find the missing side lengths. Once we identify the missing side lengths, in this case the red lines, we can start the process. One characteristic that we need to remember is that opposite sides of rectangles are the same. One of the side lengths that is missing is the 4 cm. We find that by using the 3 cm and the 7 cm because x + 3 cm = 7 cm. Remember that opposite sides are equal. So 7 is the total length of the figure, if we extend the left rectangle to the right, then we get x + 4 cm = 7 cm, and x = 4 cm.

Now the other side length that is missing is the 8 cm. We find that by using 2 cm and 6 cm because 2 cm + 6 cm = x. Once again remember that opposite sides are equal. So x is the total length, and we extend the right rectangle upward, then we get 2 cm + 6 cm = x, and x = 10 cm.

Remember perimeter is the length of all side lengths, that is why we found the missing side lengths. Now we add all 6 sides, 2 + 4 + 6 + 3 + 8 + 7 = 30 cm.

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