Pell's equation is used in mathematics when there is an equation with two or more unknowns. If you want to challenge your knowledge and test your informations, take this quiz!
Joseph Louis Lagrange
Algebraic number theory
All of the above
(x,y) = (32188120829134849,181938015856460)
(x,y) = (1,2)
(x,y) = (176619049,226153980)
(x,y) = (0,-1)
Here's an interesting quiz for you.