you're thinking about buying a house but you really want to figure out how much area does a house cover what is the the square footage of the house or what is the area of the foundation of the house so right here we have the floor plan of the house and you're tasked with finding its area and you're given the dimensions of a bunch of walls of the house this wall right here is 18 feet this is 8 feet this is 20 feet 20 feet 5 feet 26 feet 15 feet and 25 feet but you're a little confused you know how to find the area of rectangles but how do you find an area of a strange shape like this so I encourage you to pause this video and try to figure out the area of this strange house footprints shape for plan shape using the techniques that you already know about so what you already do know about is how to find the area of rectangles so if we can break this houses floorplan into a series of rectangles and find out the areas of those rectangles then we can figure out the area of this entire house so let's break it into a bunch of simpler rectangles so I could have one rectangle here it has a width of 20 feet and it has a length of 20 feet so that would be a rectangle right over there and we should be able to figure out its area then I could set up another rectangle that has a width of 26 feet and has a length that's it's length right over there and we could think about in a second what that length actually is actually let's think about that how would we figure out what this length actually is well this this length plus 5 feet is going to be the same thing as this length over here is the same as the opposite wall of this of this rectangle so this length Plus 5 feet is 20 feet well this must be 15 feet so this blue rectangle is 15 feet long and 26 feet wide now let's add another rectangle we could have one that's 18 feet long and then goes the entire length of the house goes the entire length of the house like that and you might say wait how do we figure out its width how do we figure out the width of this rectangle well we know that this is 8 feet we know that this is 20 feet and we know that this is 26 feet so the entire width is going to be 26 feet plus 20 feet so 26 plus 20 gets us to 46 plus 8 gets us to 54 feet so this is 54 54 feet right over here did I do that right let's see 8 plus 36 would be 34 plus 20 is 54 feet and then finally we have one last rectangle to deal with this rectangle right over here which is 15 feet long and 25 and 25 feet wide and so now we can calculate the areas of the different rectangles so the total area is going to be the 20 feet by the 20 feet so let's just multiply them so it's going to be 20 times 20 that's this area right over here plus 15 times 26 so plus 15 times 26 that's this area right over there plus 18 times 54 plus 18 times 54 which is this area right over there and then finally plus 15 times 25 plus 15 times 25 which is this area this area right over here so we just have to now evaluate these things so what is 20 times 20 well this is going to be 400 what's 15 times 26 let's multiply it out 26 times 15 6 times 5 is 30 2 times 5 is 10 plus 3 is 13 now I'm going to multiply a 10 times 26 gets us to 260 and you add these two together you get 390 so it's 400 plus 390 now we've got to multiply 18 times 54 54 times 18 so let's do that 54 times 18 8 times 4 is 32 8 times five is 40 plus three is 43 now we're multiplying this 10 times 54 gets us to 540 and we add 2 plus 0 is 2 this 30 plus the 40 gets us to a 70 is or it's a 3 plus a 4 in the tens place and then 400 plus 500 is 900 so we get to 972 and one more of these multiplications 25 times 25 times 15 and actually we could do that in our head this is 26 times 15 so 25 times 15 is going to be this minus 15 so it's going to be 300 you see if you subtract 10 you get to 380 subtract another 5 375 let me do it in that same color so plus plus 375 and now let's add up these numbers so we have 375 plus 972 plus three hundred and ninety 390 plus 400 plus 400 and so this gets us to five this is the homestretch we deserve a drum roll now 5 plus 2 is 7 7 plus 7 is 14 plus 9 is 23 2 plus 3 is 5 plus 9 is 14 17 21 so the square footage of this house 2137 square square feet
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and the solutions are decreasing functions.