Final answer:
The correct operation to use in the equation 2_x = 57_4 = 14.25 is division (÷) because dividing 57 by 4 gives us the decimal number 14.25.
Step-by-step explanation:
To find the missing operation sign in the equation 2_x = 57_4 = 14.25, we need to understand the rules for each operation. Since the given equation involves numbers with decimal places, we can eliminate addition and subtraction as these operations do not result in decimal numbers. Multiplication can be ruled out as well because multiplying 2 by any number will not give us a decimal answer. Therefore, the correct operation to use in this equation is division (÷), since dividing 57 by 4 gives us the decimal number 14.25.