Вариант 3 n1 1) (a-7)(b+5)=ab+5a-7b-35
2) (2a+7)(3a-5)=(6a^2-10a+21a-35)
3)(a-3b)(a^2-2ab-5b^2)=a^3-2a^2b-5b^2a-3ba^2+6ab^2+15b^3
n2
(a+3)(a-7)-4a(5-2a)=a^2-7a+3a-21-20a+8a^2=9a^2-24a-21
n3
(x+2)(x-4)-(x-5)(x-6)=3x
x^2-4x+2x-8-(x^2-6x-5x+30)=3x
x^2-2x-8-x^2+6x+5x-30=3x
9x-38-3x=0
6x=38
x=38/6=19/3