FORMULABANK

If two triangles have the same angles pairwise, they are called similar.

The ratio of the corresponding sides is the same for all sides.

In the example, the ratio between ∆ABC and ∆A₁B₁C₁ is 2
ratio=\frac{a}{a_1}=\frac{b}{b_1}=\frac{c}{c_1}