А) (2х-1)^2
б) (3а+с)^2
в) (y-5)(y+5)
г)(4b+5c)(4b-5c)

(2x - 1)^2 = 4x^2 - 4x + 1(3a + c)^2 =9a^2 + 6ac + c^2(y - 5)(y + 5) = y^2 - 25(4b + 5c)(4b - 5c) = 16b^2 - 25c^2