The third proportional to (x² − y²) and (x − y) is :

1. $\dfrac{x - y}{x + y}$

2. $\dfrac{x + y}{x - y}$

3. (x + y)

4. (x − y)

The mean proportion between 9 and 16 is:

1. 7

2. 12

3. 25

4. 144

The mean proportion between (3 + $\sqrt{2}$) and (12 − $\sqrt{32}$) is:

1. 6

2. $2\sqrt{7}$

3. $\sqrt{7}$

4. $\dfrac{15 - 3\sqrt{2}}{2}$

The mean proportion between x and y is 6. The third proportional to x and y is 48. Then x : y equals :

1. 1 : 3

2. 1 : 4

3. 1 : 6

4. 1 : 9