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;
![Geometric \ mean= √(a * b)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/3iaefr3jsjylce9bahb2v3hs31yry8djuc.png)
where a and b are two positive numbers.
Substituting Geometric mean = 12, a = 3 and b = x, we get;
![12= √(3 * x)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/37xadq5zfedl422p6gd8alhghj5ypajj8e.png)
Squaring on both sides, we get;
![12^2=3 * x](https://img.qammunity.org/2021/formulas/mathematics/middle-school/ppnpbkyte4ihxsa410wh23lmtmu8gkxfkh.png)
![144=3* x](https://img.qammunity.org/2021/formulas/mathematics/middle-school/m06pby1cfnpvdqkeuftpabcvcacsuypw67.png)
Dividing both sides of the equation by 3, we have;
![48=x](https://img.qammunity.org/2021/formulas/mathematics/middle-school/xs7oub9uu9so0wf3jygb29c9vd6adki7i1.png)
Thus, the value of x is 48.