а) (6х + 5)^2 - (4x+5)^2 = 36x^2 + 60x + 25 - 16x^2 - 40x - 25 = 20x^2+20x = 20x(x+1)
б) (2х - 3у)^2 - (5x+7y)^2 = 4x^2 - 12xy + 9y^2 - 25x^2 - 70xy - 49y^2 = -21x^2 - 40y^2 - 82xy = -(21x^2 + 70xy + 12xy + 40y^2) = -(7x(3x+10y)+4y(3x+10y)) = -(7x+4y)(3x+10y) = (7x+4y)(10y-3x)
в) (3a + 2b)^2 - (7a-6b)^2 = 9a^2 + 12ab + 4b^2 - 49a^2 + 84ab - 36b^2 = -40a^2 - 32b^2 + 96 ab =-8(5a^2 - 12ab + 4b^2) = -8(5a^2 - 10ab - 2ab +4b^2) = -8(5a(a-2b) - 2b(a - 2b)) = -8(a-2b)(5a-2b) = (a-2b)(16b - 40)