28.35
в) (у-5)^2-(у-2)=у^2+25-10у-у+2=у^2-9у+27.
28.36
а)(3а-b)(3a+b)+b^2=((3a-b))^2+b^2=9a^2+b^2-6ab+b^2=9a^2+2b^2-6ab
б)9x^2-(y-4x)(y+4x)=9x^2-((y-4x))^2=9x^2-(y^2+16x^2-8xy)=9x^2-y^2-16x^2+8xy=-y^2-7x^2+8xy
28.41
б)(x-3)^2 - (x-3)*(x+3) = (x^2 - 6x + 9) - (x^2 - 3^2) = x^2 - 6x + 9 - x^2 + 9 = -6x + 18 = -6*(-0.1) + 18 = 18.6