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Finding the surface area of 3 dimensional shapes

Grade 12 Math: Master Advanced Concepts & Skills

Geometric constructions

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Classifying triangles

Isosceles and equilateral triangles

Conics - Parabola

Conics - Circle

Conics - Ellipse

Conics - Hyperbola

Parallel and perpendicular lines

Pairs of lines and angles

Parallel lines and transversals

Parallel line proofs

Perpendicular line proofs

Circle geometry

Angles in a circle

Circles and circumference

Circle properties

Arcs of a circle

Areas and sectors of circles

Transformations of 2D shapes

Line symmetry

Rotational symmetry and transformations

Enlargements and reductions with scale factors

Scale diagrams

Similar triangles

Similar polygons

Non-Euclidean geometries

Combining transformations of functions

Surface area of 3-dimensional shapes

Transformations of functions: Horizontal translations

Transformations of functions: Vertical translations

Reflection across the y-axis: y = f(-x)

Reflection across the x-axis: y = -f(x)

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Geometry 12

math

https://dmn92m25mtw4z.cloudfront.net/img/textbook/textbook-grade12math.png

- Hi, welcome to this question right here. So what happen is we're trying to determine the dimension of this cut out piece. So we&apos;ve got a little rectangle right here, right? So we&apos;ve got all sort of information down here, so we're going to use each pieces right here to determine the dimension of this part that you're going to cut out which is this part right here. Okay? 
So let's start from the top first. So if you're looking from the top, it says now right over here on the back over here is 20. So I'm going to put a little 20 right there to remind our self, and this part right here. This part here is 15, so that's 15. Okay? So that's going to add it in. So far there isn't too much information that we have to determine the dimension of that little cut out piece. Let's go to the next one, just looking it from the left. So this is your left and side, this piece right here. That's your left hand side. So it says, if you're looking from the left. This part right here is six centimeters, so that six. So we just discovered our first dimension to the cut out piece. This bottom part right here is six. Okay? 
Then, we have nothing else. Okay, that's unfortunate but we do know that 20, that's 20, that's six. So then makes this part here 14. Okay? I don't know if we need that but, let's just put it in just in case we needed that for a later questions. Let's focus on the front. If you're looking from the front, you're looking from this way, okay? So we have the 20-- 
This side is also 20, okay. So I'm going to put a little line right there to represent that as side 20. We know that the bottom part is 27. That's your 27. We do know the next dimension now, because it looks like-- actually we do, because that's 10 right there. See this part right here, the 10? That means this part here is also 10. Okay? I kind of ran out of space, but if you just do a quick math right there. This whole thing is 20, right? That part is 10. So that makes this part here as 10 as well. Okay? That part represents this part here. So we just found out that our next dimension which is this part, that's 10. This is also 10. Okay? 
So the only thing that we're missing is actually-- 
Oh, it's not missing, it's actually-- We know this side, the whole thing is 27, right? Now, if you take that 27 and subtract the 15 on the top, you get yourself just the 12. Okay? That 12 will go right there. So we just figure out our last dimension right here which is 12, okay? So six times 12, times 10 for this cut out piece and if you want to figure out the area right now. Six time 12 times the 10, we&apos;ve got our area turns out to be-- 
Just let me fill the work here, which is length times the width times the height, right? So we&apos;ve got ourselves six times the 12, times the 10. We have 720, okay? 
So that 720 is the area and the dimension for this question, it's six time 10, times the 12. Then let's quickly go to the next question and see what they're asking for. They're looking for-- Just let me see, so I'll remember it. We still have the dimension of 720, right? But as you can see, the next question says, "How does the surface area of the original rectangle object change after cutting out that corner piece?" 
Well, this question here doesn't really need the calculation because if you think about it, the surface area did not change at all. Okay? So the answer to that question right now, I want to say there's no change. Now, you'll probably thinking like, "Okay, how is that possible?" 
Because you cut out a one piece from the original rectangle, right? This piece has been cut out, but surface area is different from the volume. Surface area is we look at an object from all the surfaces, right? So if you just imagine, if you look at this cut out pieces right now, then other cut out piece, this diagram right here with all these dimensions. If you're looking from the top, you still see a perfect rectangle. If you look at it from the left that it's still a perfect rectangle. If you see it from the right which is still a rectangle, right? When you're seeing right here, it's the same as before. Okay, because when you look at it from-- 
Let's say if you're looking from the top, you still see the surface-- Let me just erase all these right here. You still see all the surface area, including that little piece down here. So the surface area actually didn't change from before and after. So that's why the surface area of the original rectangle object did not change even after you cut it out, okay? 
Only the volume changes, okay? Hoping that it make sense. Thanks for watching.

In this section, we will learn how to calculate the surface area of 3D objects. We will also look further into the subject ? What would happen to the surface area if the shapes are 
cut into pieces? How about a piece is cut out of the shape? 

Introduction to surface area of 3-dimensional shapes

Nets of 3-dimensional shapes

Surface area of prisms