Final answer:
The correct symbols to finish the statement '1-21_' comparing 1 and -21 are '>' (greater than) and '≠' (not equal to), because 1 is greater than -21.
Step-by-step explanation:
The original statement is 1-21 with a blank after it, where we need to place the appropriate symbol. To determine which symbols could finish the statement correctly, we should compare the values. The first value is 1, and the second value is -21. Since 1 is greater than -21, the correct symbols that could be used to complete the statement are '>' (greater than) or '≠' (not equal to), because 1 is neither less than nor equal to -21.