If x = $(3 + \sqrt{8})$, find the values of $\Big(x^2 + \dfrac{1}{x^2}\Big)$.

If x = $(4 - \sqrt{15})$, find the values of $\Big(x^2 + \dfrac{1}{x^2}\Big)$.

Which of the following is an irrational number?

1. 2.7

2. $2.7\overline{2}$

3. $\sqrt{11}$

4. $\dfrac{2}{7}$

Which of the following is a prime number?

1. 51

2. 57

3. 71

4. 81