Your task is to create independent triangles (which means they do not have the same edge) by drawing straight lines as exemplified below:

enter image description here

In this example, there are $5$ lines and $5$ independent triangles and no triangle exists with the same edge with another triangle.


At least how many straight lines do you need to have $11$ independent triangles without having any triangle having the same edge as given above?

  • $\begingroup$ Is Independent triangles means there is at least one edge that is not touched by another triangle? $\endgroup$
    – rudra
    Dec 2, 2017 at 14:04
  • $\begingroup$ @rudra no edge is supposed to be common between two triangles at all in the graph. $\endgroup$
    – Oray
    Dec 2, 2017 at 14:06
  • $\begingroup$ It seems 12 independent lines are required though they can form 12 such triangles instead of required 11 :-( $\endgroup$ Dec 2, 2017 at 14:30
  • $\begingroup$ Doing some search Oray, isnt KOBON triangle same as what you are asking? $\endgroup$
    – DrD
    Dec 2, 2017 at 14:58
  • $\begingroup$ @DEEM yes :) but asking this as a question is a puzzle itself. $\endgroup$
    – Oray
    Dec 2, 2017 at 14:59

2 Answers 2


I created 11 independent triangles with ...

... 7 lines:



with 7 lines enter image description here could be same as the previous answer

  • $\begingroup$ I got this before seeing previous answer. However I also found that something like this is defined as KOBON triangles? I may be wrong $\endgroup$
    – DrD
    Dec 2, 2017 at 15:00

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