Answer:
Nikolai Lobachevsky and Bernhard Riemann
Step-by-step explanation:
Nikolai Lobachevsky (A russian mathematician born in 1792) and Bernhard Riemann (A german mathematician born in 1826) are the mathematicians that helped to discover alternatives to euclidean geometry in the nineteenth century.
The external angle is suplementary to the internal angle close to it. We also know that the sum of all the internal angles of the triangle are equal to 180 degrees, this means that the angle "a" is suplementary to the sum of the angles "b" and "c". Through this logic, we can conclude that since:

Then we can conclude that:

Therefore the statement is true, the exterior angle is equal to the sum of its remote interior angles.
Let's use an example:
On this example, the external angle is 120 degrees, therefore the sum of the remote interior angles must also be equal to that. Let's try:

The sum of the remote interior angles is equal to the external angle.
So-called simplifying, really means, "rationalizing the denominator", which is another way of saying, "getting rid of that pesky radical in the bottom"
In order from left to right its RRRT
R is repeating and T is terminating