Solution to the triangle puzzle


** Note: Some posts on Math-Fail are user-submitted and NOT verified by the admin of the site before publication. If you find this post to be distasteful, non-math related, ?or something worse?, then definitely leave a comment letting me know. Thanks very much! Mike **

1 Star2 Stars3 Stars4 Stars5 Stars (4.13 from 16 votes)


  1. The two big triangles are not the same. The red triangle has a slope of 3/8 but the teal triangle has a slope of 2/5. This means the “hypotenuse” of the big triangle is not a straight line. It bulges in in the first big triangle then bulges out in the second big triangle to make room for the extra space.

    Thumb up 2 Thumb down 0


    Go here for an interactive version of this triangle which makes it much easier to see what’s going on.

    Thumb up 2 Thumb down 0

  3. In other words, the 1st large triangle is not a triangle at all. What appears to be the hypotenuse of a right triangle is, in fact, two sides of a quadrilateral. They just happen to meet at an angle of 181.2º – so close to 180º that it’s indistinguishable to the eye. I love it.

    Thumb up 0 Thumb down 0

  4. Everyone already knew this.

    Thumb up 0 Thumb down 0