A poster purporting to explain the convenient distance between four people to avoid COVID-19 contagion sparked laughter on Twitter for a curious mistake that would blush Pythagoras.

A Brazilian mathematician explained the ruling and drew the strange way four individuals must be positioned to meet the required distance.

The COVID-19 pandemic made everyone should learn a little more biology, a little more epidemiology and a little more health resource management. And it’s not the only thing coronavirus can teach us, as the need to maintain social distancing may also require us to learn a little more math.

It all started, of no other means, on social media, when the image of a poster that was trying to explain how four people should be positioned in the space so that they were all 1.5 meters away from each other but who made a fundamental mistake.

“A minute’s silence for Pythagoras”, lamented the tweeter who viralized the image, giving rise to an extensive thread of responses in which users shared their disappointment at the failed sketch.

The debate caught the attention of Brazilian professor of Mathematics at the University of Campinas (Unicamp) Marcos Henrique de Paula Dias da Silva, who dedicated a post on his blog Zero to explain why the image constitutes a mistake.

The teacher consigned that the arrangement of the people allows making a right triangle between three of the four figures. The problem arises when the drawing itself indicates that the legs of that triangle are worth 1.5 but the hypotenuse is also worth 1.5 meters.

“If all three sides are the same, then it’s not a right triangle but an equilateral,”

the professor said, stressing that

“three people can be equidistant on a plane at 1.5 meters each but in the figure we have four people and that complicates the thing.”

The reference to Pythagoras—the Greek philosopher and mathematician of the 5th century BC—comes from the fact that it is the Pythagorean Theorem allows determining the measurement of the hypotenuse from the cathetus and vice versa. In this case, if the cathetus of a right triangle measure 1.5, the hypotenuse should measure 2.12. If instead, it is the hypotenuse that measures 1.5, the cathetus will necessarily have to measure 1.06.

For the teacher, if we had to choose, it would be better if the value of 1.5 corresponded to the legs, as it would ensure a greater distance between the parties.

Not satisfied with his explanation, the professor revealed that there is a way for four people to be equidistantly 1.5 meters away. Actually, this cannot be possible if it is a plane but in a three-dimensional space.

“In this case, to consider the correct initial image, we would need to imagine that the four people were each at a vertex of a regular tetrahedron (a triangular-based pyramid in which all their sides or faces have the same size)”

he illustrates

While it would seem like a complicated distribution for four people to sit in a bar, the teacher’s explanation is helpful, not only to understand why the image went viral, but also to understand how math can be crucial in combating coronavirus.