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Today I?m going to talk about Finding area by decomposing rectangles.
So in this example, we have a large rectangle with a smaller rectangle cut out of it.
They are asking us to find the area of the shaded figure so I have colored in this part.
This part is not.
So we are only wanting to find the area of this part.
So the good part is that we do know the full size of the rectangle. It?s 9 cm by 7 cm. So if we start out with that shape, we could get that area.
And we take the area, 9x7 equals 63. That is the area of this whole shape. If the shape was still in there, not cut out.
So, I?m going to put 63 here down in my equation.
Alright, so now we have 63 minus something equals the total sq. cm.
So if we had this, and if we had to physically remove the area of this little shape, we will have to find the area of this little shape.
And we figure that out by multiplying the two sides.
3x2 equals 6. So I?m going to put that.
Now that I?ve got 2 values.
So now I?m going to subtract, 63 minus 6.
I?m going to put that on top of each other.
So we barrow. 13 minus 6 is 7. So we bring the 5 down. It?s 57.
So 63 minus 6 is 57 sq. cm.
So the area is 57 sq. cm.
Again, that was Finding area by decomposing rectangles.
Brief lesson/example of how to solve for area by decomposing new rectangles.