Упростит выражение 1) (a+5)(a-2)+(a+4)(a-5) 3) (2x-3y)(2x+3y)+(3x+2y)(3x-2y) 5)...

1) (a+5) (a-2) + (a+4) (a-5) = $a^{2}$ - 2a + 5a - 10 + $a^{2}$ - 5a + 4a - 20 = $2a^{2}$ + 2a - 30
3) (2x-3y)(2x+3y)+(3x+2y)(3x-2y) = $4x^{2}$ - $9y^{2}$ + $9x^{2}$ - $4y^{2}$ = $13x^{2}$ - $13y^{2}$
5) (y-4)(y+3)-(y-6)^2 = $y^{2}$ + 3y - 4y - 12 - ( 2y - 12 ) = $y^{2}$ + 3y - 4y - 12 - 2y + 12 = $y^{2}$ - 3y