Exercise 3.79: Generalize the solve-2nd
procedure of Exercise 3.78 so that it can be used to solve general
second-order differential equations 
  
    
      d
      2
    
    y
    
      /
    
    d
    
      t
      2
    
  
  =
  
    f
    (
    d
    y
    
      /
    
    d
    t
    ,
    y
    )
  
.