If x + y = 18 and xy = 72, what is the value of x2 + y2?

Given in question,
x + y = 18
By using algebraic formula
∵ x² + y² = (x + y)² - 2xy
Put the value of x + y and xy as per given question,
⇒ x² + y² = (18)² - 2 x 72
⇒ x² + y² = 324 - 144
⇒ x² + y² = 180