Найдите значение выражения:
а) $a^2 + ab - 7a - 7b$ при a = 6,6, b = 0,4;
б) $x^2 - xy - 4x + 4y$ при x = 0,5, y = 2,5;
в) $5a^2 - 5ax - 7a + 7x$ при a = 4, x = −3;
г) xb − xc + 3c − 3b при x = 2, b = 12,5, c = 8,3;
д) ay − ax − 2x + 2y при a = −2, x = 9,1, y = −6,4;
е) 3ax − 4by − 4ay + 3bx при a = 3, b = −13, x = −1, y = −2.
при a = 6,6, b = 0,4:
$a^2 + ab - 7a - 7b = (a^2 - 7a) + (ab - 7b) = a(a - 7) + b(a - 7) = (a - 7)(a + b) = (6,6 - 7)(6,6 + 0,4) = -0,4 * 7 = -2,8$
при x = 0,5, y = 2,5:
$x^2 - xy - 4x + 4y = (x^2 - xy) - (4x - 4y) = x(x - y) - 4(x - y) = (x - y)(x - 4) = (0,5 - 2,5)(0,5 - 4) = -2 * (-3,5) = 7$
при a = 4, x = −3:
$5a^2 - 5ax - 7a + 7x = (5a^2 - 5ax) - (7a - 7x) = 5a(a - x) - 7(a - x) = (a - x)(5a - 7) = (4 + 3)(5 * 4 - 7) = 7(20 - 7) = 7 * 13 = 91$
при x = 2, b = 12,5, c = 8,3:
xb − xc + 3c − 3b = (xb − xc) − (3b − 3c) = x(b − c) − 3(b − c) = (b − c)(x − 3) = (12,5 − 8,3)(2 − 3) = 4,2 * (−1) = −4,2
при a = −2, x = 9,1, y = −6,4:
ay − ax − 2x + 2y = (ay − ax) + (2y − 2x) = a(y − x) + (y − x) = (y − x)(a + 2) = (−6,4 − 9,1)(−2 + 2) = −15,5 * 0 = 0
при a = 3, b = −13, x = −1, y = −2:
3ax − 4by − 4ay + 3bx = (3ax + 3bx) − (4ay + 4by) = 3x(a + b) − 4y(a + b) = (a + b)(3x − 4y) = (3 − 13)(3 * (−1) − 4 * (−2)) = −10 * (−3 + 8) = −10 * 5 = −50
Пожауйста, оцените решение
