ruby - Why does the Array allocation my_arr[0,3] work while my_arr[3,0] fails? -

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I want to draw two values ​​from one array based on their parameters. My_array [1,2] # = & my_array = ["a", "b", "c", "d", "e", "f", "g"]

Why is the final allocation failing to remove elements of 2 and 0?

I suspect that my operation really is not what I think is actually doing, because by connecting the third index, the whole thing fails: 

  My_array [1,2,3] # = & gt; ArgumentError: Wrong number of arguments (1..2 for 3)   
 What am I really doing with syntax [var1, var2] and what should I do?   
 
 
  piece  syntax:  
 
   
 This is a small syntax for  my_array.slice (start, length);   
 You should do this instead:  
  my_array.values_at (2, 0) => ["C", "A"]   
 and

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