Answer:
a = 36 and a = 27
Explanation:
The geometric mean of two numbers is the square root of the product of the two numbers.
Say for example we have the numbers x and y, the geometric mean z is mathematically;
z = √xy
For the first question, our z is 12, x and y are 4 and a respectively.
12 = √4a
square both sides
144 = 4a
a = 144/4
a = 36
For the second question
z is 9, x and y are 3 and a respectively
9 = √3a
square both sides
81 = 3a
a = 81/3
a = 27