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# Perimeter & area of composite shapes

Sal finds perimeter and area of a non-standard polygon. Created by Sal Khan and Monterey Institute for Technology and Education.

Video transcript

Find the area and the perimeter of the polygon so lets start with the area first so the area of this polygon and there's kind of two parts to this first you have this part that's kind of rectangular or it is rectangular this part right over here and that area is pretty straightforward it's just going to be base times height so the area's going to be 8 times 4 8 times 4 for the rectangular part and then we have this triangular part up here so we have this area up here and for a triangle this area is base times height times 1/2 that actually makes a lot of sense because you just multiply base times height you would get this entire area you get the area of the entire rectangle and you see that the triangle is exactly half of it if you took this part of the triangle and you flip it over, you'd fill up that space and you took this part of the triangle and you flip it over, you'd fill up that space so the triangle's area is half of the triangle's base times the triangle's height so plus 1/2 times the triangles base which is 8 inches and the triangles height which is 4 inches. so let us calculate it this gives us it is not 4, triangles height is 3, so let us go back and calculate it area = 32 + 1/2 * 8*3 = 32 + 12 = 44 area of the figure is 44 now let us do the perimeter.We need to figure out the sum of the sides. If we need to put a fence what is the length that we need to cover so the perimeter = 8+4+5+5+4 =26 inches Let me get the unit right, here we are multiplying 8 inches by 4 inches we get 32 square inches and here we multiply 8 inches by 3 inches we get 24 square inches divide by 2 we get 12 square inches. area = 44 square inches, perimeter is 26 inches area is two dimensional and perimeter is one dimensional