Given:
The number 12 is the geometric mean between 3 and a number x.
We need to determine the value of x.
Value of x:
Since, we know that the geometric mean is the square root of the product of two numbers.
Hence, we have;

where a and b are two positive numbers.
Substituting Geometric mean = 12, a = 3 and b = x, we get;

Squaring on both sides, we get;


Dividing both sides of the equation by 3, we have;

Thus, the value of x is 48.