ГДЗ по алгебре 7 класс Макарычев Задание 790

\[\boxed{\text{790\ (790).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]

Пояснение.

Решение.

\[\textbf{а)}\ a^{2} + ab - 7a - 7b =\]

\[= a(a + b) - 7 \cdot (a + b) =\]

\[= (a + b)(a - 7)\]

\[если\ a = 6,6;\ \ \ b = 0,4:\]

\[(6,6 + 0,4)(6,6 - 7) =\]

\[= 7 \cdot ( - 0,4) = - 2,8\]

\[\textbf{б)}\ x^{2} - xy - 4x + 4y =\]

\[= x(x - y) - 4 \cdot (x - y) =\]

\[= (x - y)(x - 4)\]

\[если\ x = 0,5;\ \ \ y = 2,5:\]

\[(0,5 - 2,5)(0,5 - 4) =\]

\[= - 2 \cdot ( - 3,5) = 7\]

\[\textbf{в)}\ 5a^{2} - 5ax - 7a + 7x =\]

\[= 5a(a - x) - 7 \cdot (a - x) =\]

\[= (a - x)(5a - 7)\]

\[если\ \ a = 4;\ \ x = - 3:\]

\[(4 + 3)(5 \cdot 4 - 7) =\]

\[= 7 \cdot (20 - 7) = 7 \cdot 13 = 91\]

\[\textbf{г)}\ xb - xc + 3c - 3b =\]

\[= x(b - c) - 3 \cdot (b - c) =\]

\[= (b - c)(x - 3)\]

\[если\ x = 2,\ b = 12,5;\ \ c = 8,3:\]

\[(12,5 - 8,3)(2 - 3) =\]

\[= 4,2 \cdot ( - 1) = - 4,2\]

\[\textbf{д)}\ ay - ax - 2a + 2y =\]

\[= a(y - x) + 2 \cdot (y - x) =\]

\[= (y - x)(a + 2)\]

\[если\ a = - 2;\ \ x = 9,1;\ \ \]

\[y = - 6,4:\]

\[( - 6,4 - 9,1)( - 2 + 2) =\]

\[= - 15,5 \cdot 0 = 0\]

\[\textbf{е)}\ 3ax - 4by - 4ay + 3bx =\]

\[= 3x(a + b) - 4y(a + b) =\]

\[= (a + b)(3x - 4y)\]

\[если\ \ a = 3;\ \ b = - 13;\ \ x = - 1;\ \]

\[\ y = - 2:\]

\[(3 - 13)\left( \ 3 \cdot ( - 1) - 4 \cdot ( - 2) \right) =\]

\[= - 10 \cdot ( - 3 + 8) = - 10 \cdot 5 =\]

\[= - 50\]