Final answer:
To make the sentence true, use the symbol "<" to compare the square roots of 50 and 78.
Step-by-step explanation:
To determine which symbol makes the sentence “true”, we need to compare the values of the square root of 50 and the square root of 78. We can do this by simplifying both square roots. The square root of 50 is approximately 7.07, and the square root of 78 is approximately 8.83. Comparing these values, we can see that 7.07 is less than 8.83. Therefore, the correct symbol to make the sentence true is “<” (less than).