__ n=3                  n-k k
B(t)     = ❯     \ P  \binomnk(1-t)   t                
    cubic  ‾‾ k=0    
                    k
                                                       
                   3            2             2       3
         = P  (1-t)  + 3 P (1-t) t + 3P (1-t)t  + P  t 
                                                    
            0             1            2           3