1) 6x² + (2y-3x) (2y+3x)

2) (a+2) (a-3) - (4-a) (a+4)

3) (5-2x) (5+2x) - (3-2x) (4-2x)

1) 6x² + (2y-3x) (2y+3x) = 6x² + (4y²+6xy-6xy-9x²) = 6x²+4y²-9x²=4y²-5x²

2) (a+2) (a-3) - (4-a) (a+4) = a²-3a+2a+6 - (4a+16-a²-4a) = a²-a+6-4a-16+a²+4a=

=2a²-a-10

3) (5-2x) (5+2x) - (3-2x) (4-2x) = 25+10x-10x-4x² - (12-6x-8x+4x²) =

=25-4x²-12+14x-4x²=-8x²+14x+13