Who is one of the scientists who proved the theorem that the sum of the angles of a triangle is 180 degrees.

For the first time this theorem was deduced by Euclid;

The following corollaries follow from this theorem;

Corollary 1. The sum of the acute angles of a right-angled triangle is 90 °.

Corollary 2. In an isosceles right-angled triangle, each acute angle is 45 °.

Corollary 3. In an equilateral triangle, each angle is 60 °.

Corollary 4. In any triangle, either all the corners are acute, or two corners are acute, and the third is obtuse or straight.

Corollary 5. The external angle of a triangle is equal to the sum of two internal angles that are not adjacent to it.