Question

If three corresponding sides of one triangle are proportional to three sides of another, then the triangles are similar. always sometimes never

Answer 1

If all 3 sides are proportional, then they are always similar. 

The definition of similar triangles is that they are proportional on all sides and angles. 

Answer 2

If three corresponding sides of one triangle are proportional to three sides of another, then the triangles are similar 'Always'.

As, we know that the two triangle are only similar when there corresponding sides is equal to one another. (This is the definition of similar triangle.)