Figures are mathematically similar when..

When all of the corresponding angles are congruent.

When there is a scale factor between the two shapes.

True or False

Any two rectangles are similar :

1) All the angles are the same (90 degrees).
2) If you have two rectangles, the sides of one could be 1 and 2 units. For the other they could be 1 and 3 units. The sides do not have the same proportions. One is 1:1 and the the other is 2:3.
So rectangles are not all similar.

Any two equilateral triangles are similar :

For the equilateral triangles since they always have 3 angles that are each 60°, any 2 equilateral triangles will be similar.

The left is the bad notes because there is to much highlight and hard to read.

The right is good notes because they are clear and organized.