A)
(x + y)² = x² + 2xy + y²
=> x² + y² = (x + y)² - 2xy = 7² - 2 × 8 = 49 - 16 = 33
B)
(x - y)² = x² - 2xy + y²
=> x² + y² = (x - y)² + 2xy = (3√3)² + 2 × 12 = 27+ 24 = 51
C)
(x + y)² = x² + 2xy + y²
=> x² + y² = (x + y)² - 2xy = (3√5)² - 2 × 0 = 45 - 0 = 45