Finding the missing lengths in similar figures is exactly the same as finding scale as we talked about in day 2. You have to put the smaller length from the figure that has two sides that are labeled with numbers. Then you put the length that is larger from the shape that is incomplete as talking about side lengths labled. You put them next to each other and cross multiply to get something that looks like this: #x=#, so a number times x is equal to a number.
Quiz
1. Find the missing length:
2. Does it matter if you put the smaller or larger number over the other?
3. Does this system work for all shapes?
Answer key
1. The missing length would be 21cm. To get this you would have to put 6 over 9 equals 14 over x. After you cross multiply, you should end up with 6x is equal to 126. You then divide 126 by 6, which should give you 21 cm.
2. It does not matter if you put the smaller or larger on top, but you do have to do the same for both. For example, from question 1, it doesn't matter if you did 6 over 9 or 9 over six, as long as you did 14 over x so it matches smaller side over longer side, or x over 14.
3. Yes this system will work for all shapes, except for circles. Circles are a whole different thing.
Commented on Franks blog.
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