3) (2 - 3х)(5х - 3) - х(2 - х) = 3 - 12х²,
10х - 6 - 15х² + 9х - 2х + х² - 3 + 12х² = 0,
-2х² + 17х - 9 = 0,
2х² - 17х + 9 = 0,
a = 2, b = -17, c = 9;
4) (1 - 2x)(2x - 4) - 3(2 - x) = 3 - 9x²,
2x - 4 - 4x² + 8x - 6 + 3x - 3 + 9x² = 0,
5x² + 13x - 13 = 0,
a = 5, b = 13, c = -13;
5) (5 + 2x)(4x - 1) - 2(2 + 3x) = -13x²,
20x - 5 + 8x² - 2x - 4 - 6x + 13x² = 0,
21x² + 12x - 9 = 0,
7x² + 4x - 3 = 0,
a = 7, b = 4, c = -3;
6) (2 - 6x)(x - 4) - 3x(1 - x) = -22x²,
2x - 8 - 6x² + 24x - 3x + 3x² + 22x² = 0,
19x² + 23x - 8 = 0,
a = 19, b = 23, c = -8.
Вот накалякал. Разбирайся :)
xy/(x+y) = 5
xz/(x+z) = 7
yz/(y+z) = 9
xy = 5x + 5y
xz = 7x + 7z
yz = 9y + 9z
x(y-5) = 5y
x = 5y/(y-5)
5yz/(y-5) = 35y/(y-5) + 7z
5yz = 35y + 7z * (y-5)
5yz = 35y + 7yz - 35z
2yz + 35y = 35z
y(2z + 35) = 35z
y = 35z/(2z + 35) = z/(2z/35 + 1)
35z^2/(2z + 35) = 315z/(2z + 35) + 9z
35z^2 = 315z + 9z*(2z + 35)
35z^2 = 315z + 18z^2 + 315z
17z^2 = 630z
z=630/17
y = 35*630/(2*630/17 + 35)/17 = 35*630/(1260 + 595) = 22050/1855 = 630 / 53
x = 5*630/(630/53 - 5)/53 = 5*630/((630/53 - 5)*53) = 5*630/365 = 630/73
