method: A method for approximating function in differential equations.
problem: 2 fixed centers problem related to gravity and movement in the cartesian plane.
relation: e^(i*pi)+1=0.
actually it could also be euclid, but you are probably thinking of euler.
euclid:
Method: Eucliding method for prime factorization
Problem: Euclid's 47th problem is pretty famous, it is the same as the Pythagorean theorm, but Euclid was the first to publish it
Relation: In any map on a sphere, the number of countries plus the number of vertices exceeds the number edges by 2