In the general formula for a geometric (exponential) sequence given by \( a_n = a_1 \cdot r^{(n-1)} \):
- \( a_1 \) represents the first term of the sequence,
- \( r \) is the common ratio, and
- \( n \) is the term number.
In the context of the bacteria population:
- The initial population of bacteria (when \( n = 1 \)) is given as 50. Therefore, \( a_1 = 50 \).
- The population quadruples daily, which means the common ratio \( r = 4 \).
Thus, the value of \( a_1 \) is 50.