in college courses in the theory of equations the student sometimes encounters Euler’s method for solving quartic equations, and in even the most elementary course in number theory one meets Euler’s theorem and the Euler ∅ -function( see Problem Study 10.8 ). The beta and gamma functions of advanced calculus are credited to Euler, though they were adumbrated by wallis. Euler employed the idea of an integrating factor in the solution of differential
Equations, was one of the fields to develop a theory of continued fractions, contributed to the fields of differential geometry and the calculus of variations, and considerably enriched number theory. In one of his smaller papers occurs the relation