Definition: Similar figures are figures that are the exact same shape, but are different sizes.
Two figures are similar if the lengths of their corresponding sides form a proportion. 
Example 1
These two triangles are similar. We can prove that they are similar using a ratio table to compare the lengths of their corresponding sides.
Big triangle 
Small triangle 
20  15 
8  6 
16  12 
Since all three ratios are equivalent, then the two triangles are similar.
$\frac{15}{20}=\frac{6}{8}=\frac{12}{16}$ Therefore, the two triangles are similar. 
Directions:


Example 2
These two triangles are similar. Find the missing length.
To find the missing length we need to create a ratio table, like so...
Big triangle  Small triangle 
10  6 
25 
Once the table is made, it is up to you to figure out this missing value. In this case, the missing value is 15 cm. Can you see how to get that answer?
Need a hint? [show the hint]
Directions:

Question 1 These two triangles are similar. Find the missing length.

[show answer] 
Question 2 These two rectangles are the same shape, but one has been scaled up in size. What is the missing length of the larger rectangle

[show answer] 
Question 3 Suppose a triangle is placed into a photocopier machine and a copy is made that has been reduced in size by some scale factor. Find the length of y.

[show answer] 