Question

(x+y)^2 - (3x+y).(3x+2y) =?

Answer 1

x² + 2xy + y² - [9x² + 6xy + 3xy + 2y²] = 
x² + 2xy + y² - 9x² - 6xy - 3xy - 2y² = 
x² - 9x² + 2xy - 6xy - 3xy + y² - 2y² = - 8x² - 7xy - y²