Gelfand, I M <br/><br/>
Calculus of variations 

 -  Dover  New York  1991 
 - vii, 232p.   
<br/><br/> Reprint year 2000. Includes bibliographical references and index. 
<br/><br/><label>ISBN: </label>9780486414485 
<br/><br/><label>Subjects--Topical Terms: </label><br/>Calculus  Variations<br/>Euler equations  Canonical form<br/>Mathematics<br/>Variational problems