Yes.
He created a proof.
Pythagoras' theorem is only theorem regarding right angle triangles but it is true.
To know about Pythagoras theorem in detail
There are 19 various aspects of Pythagoras theorem. Pythagorean Theorem (1) Pythagoras Theorem(2) Pythagorean Theorem (3) Pythagorean Theorem (4) Pythagoras Theorem(5) Pythagorean Theorem(6) Pythagrean Theorem(7) Pythagoras Theorem(8) Pythagorean Theorem (9) Hyppocrates' lunar Minimum Distance Shortest Distance Quadrangular Pyramid (1) Quadrangular Pyramid (2) Origami Two Poles Pythagoras Tree(1) Pythagoras Tree(2) Theorem by Pappus
Yes, the distance formula for a line segment was derived from Pythagoras' theorem.
Pythagoras' theorem is applicable to right angle triangles
~The Pythagoras theorem
Pythagoras was a Greek philosopher and mathematician who proved the Pythagorean theorem; considered to be the first true mathematician (circa 580-500 BC)
Pythagoras invented the Pythagoras Theorem.
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it relates to pythagoras theorem.
It can be proven to an extent but if the sides of a right angle triangle are equal in length then using Pythagoras' theorem is impossible to exactly find the length of its hypotenuse which will always be an irrational number that can't be determined.It is a theorem, not a theory. They are not the same. A theorem is shown to be true based on axioms, what is already known to be true. It does not need to be proven using a scientific method.