Final answer:
To find the value of a, substitute the values from point A(3,128) into the exponential function y=a·2^x and solve for a, which in this case results in a value of 16.
Step-by-step explanation:
The value of a in the exponential function y = a·2^x that passes through the point A(3,128) can be found by substituting the x and y values from the point into the equation and solving for a.
Thus, we get:
128 = a·2^3
128 = a·8
Now, we divide both sides of the equation by 8 to solve for a:
a = 128 / 8
a = 16
Therefore, the correct answer is A. 16.