When you are finding similar figures you must compare each line length of both figures to see if they are equal. In the figure above shows two triangles, To find out if they are similar we would have to find the length of each corresponding side to see if their numbers match. For example AB is equal to A'B'. AB=1 1\2, while A'B'=3. These are in unit squares. So now we have the first numbers 1 1\2 over 3. Now we figure out AC and A'C'. AC=1 1\2 while A'C'=4. You can stop here because the numbers don't match. 1 1\2 over 3 is not equal to 1 1\2 over 4. If the numbers did match then you would keep on going until all of the sides match in the numbers. Now these triangles are not similar.