Similar triangles:
The second criterion of similarity.
4th year of secondary education - Option A.
 
The second criterion of similar triangles.

Two triangles are similar if all three pairs of sides are in the same ratio.

We call the quotient obtained by comparing these corresponding sides the ratio of similitude.

Change the size of the triangles by dragging the red points with the mouse. You can also alter the value of angles B and C.

Activity 4.

The lengths of the sides of two triangles are indicated below. Check to see if they are similar and work out the ratio of similitude.

a) 8 cm, 10 cm, 12 cm
b) 52 cm, 65 cm, 78 cm
Activity 5.

A triangle has sides that are 3 cm, 4 cm and 5 cm long and we want to make a bigger triangle by enlarging the scale 3:1. How long is each side? What is the ratio of similitude?

Change the size of the triangles by dragging points C or F with the mouse.
Activity 6.

Find out whether the triangles in this window are similar or not. If they are work out the ratio of similitude. Repeat the exercise several times moving the control keys.

       
           
  Máximo Prudencio Conejo
 
Spanish Ministry of Education. Year 2001