If x + y = 8 and xy = $3\dfrac{3}{4}$, find the values of

(i) x - y

(ii) 3(x² + y²)

(iii) 5(x² + y²) + 4(x - y).

If x² + y² = 34 and xy = $10\dfrac{1}{2}$, find the value of 2(x + y)² + (x - y)².

If 2a - 3b = 3 and ab = 2, find the value of 8a³ - 27b³.

If $x + \dfrac{1}{x}$ = 4, find the values of

(i) $x^2 + \dfrac{1}{x^2}$

(ii) $x^4 + \dfrac{1}{x^4}$

(iii) $x^3 + \dfrac{1}{x^3}$

(iv) $x - \dfrac{1}{x}$.