1) (2x - 7y)(4x + 3y) = 8x^2 + 6xy - 28xy - 21y^2 = 8x^2 - 22xy - 21y^2;
2) (5x - 3y)^2 = 25x^2 - 30xy + 9y^2.
1) (2x - 7y)(4x + 3y) = 8x^2 + 6xy - 28xy - 21y^2 = 8x^2 - 22xy - 21y^2;
2) (5x - 3y)^2 = 25x^2 - 30xy + 9y^2.