A) (2а+3)(2а-3)=4a^2 - 6a + 6a - 9 = 4a^2 - 9
б) (у-5b)(у+5b)= y^2 + 5by -5by -25b^2 = y^2 - 25b^2
в) (0,8х+у) (у-0,8х) = 0.8xy - 0.64x^2 + y^2 - 0.8xy = y^2 - 0.64x^2
г) (b+0,5)^2= (b+0,5)*(b+0,5) = b^2 + b + 0.25
д) (а-2х) ^2= (а-2х) *(а-2х) = a^2 - 2ax - 2ax +4x^2 = a^2 - 4ax +4x^2
е) (ab-1)^2 = (ab-1)*(ab-1) = a^2 + ab + ab + b^2 -ab +1 = a^2 + b^2 + ab +1