Two figures are said to be similar if they are the same shape. In more mathematical language, two figures are similar if their corresponding angles are congruent, and the ratios of the lengths of their corresponding sides are equal.
This common ratio is called the scale factor.
The symbol ~ is used to indicate similarity.
In the figure below, pentagon ABCDE ~ pentagon VWXYZ.
(Note that the order in which you write the vertices matters; for instance, pentagon ABCDE is not similar to pentagon VZYXW.)
The two cylinders are similar. Find the scale factor and the radius of the second cylinder.
The height of the cylinder on the right is 1/3 the height of the cylinder on the left. So, the scale factor is 1/3.
To get the radius of the smaller cylinder, divide 1.8 by 3.
So, the radius of the smaller cylinder is 0.6 cm.