647. Найдите корень уравнения: а) 3x(2x-1) - 6x(7+x) = 90; б) 1,5x(3+2x) = 3x(x+1) - 30; в) 5x(12x-7) - 4x(15x-11) = 30 + 29x; г) 24x - 6x(13x-9) = -13 - 13x(6x-1). 648. Решите уравнение: а) 3(-2x+1) - 2(x+13) = 7x - 4(1-x); б) -4(5-2a) + 3(a-4) = 6(2-a) - 5a; в) 3y(4y-1) - 2y(6y-5) = 9y - 8(3+y); г) 15x + 6x(2-3x) = 9x(5-2x) - 36.

### 647. Найдите корень уравнения: а) $3x(2x-1) - 6x(7+x) = 90$ $6x^2 - 3x - 42x - 6x^2 = 90$ $-45x = 90$ $x = -2$ б) $1,5x(3+2x) = 3x(x+1) - 30$ $4,5x + 3x^2 = 3x^2 + 3x - 30$ $4,5x = 3x - 30$ $1,5x = -30$ $x = -20$ в) $5x(12x-7) - 4x(15x-11) = 30 + 29x$ $60x^2 - 35x - 60x^2 + 44x = 30 + 29x$ $9x = 30 + 29x$ $-20x = 30$ $x = -1,5$ г) $24x - 6x(13x-9) = -13 - 13x(6x-1)$ $24x - 78x^2 + 54x = -13 - 78x^2 + 13x$ $78x = -13 + 13x$ $65x = -13$ $x = -0,2$ ### 648. Решите уравнение: а) $3(-2x+1) - 2(x+13) = 7x - 4(1-x)$ $-6x + 3 - 2x - 26 = 7x - 4 + 4x$ $-8x - 23 = 11x - 4$ $-19x = 19$ $x = -1$ б) $-4(5-2a) + 3(a-4) = 6(2-a) - 5a$ $-20 + 8a + 3a - 12 = 12 - 6a - 5a$ $11a - 32 = 12 - 11a$ $22a = 44$ $a = 2$ в) $3y(4y-1) - 2y(6y-5) = 9y - 8(3+y)$ $12y^2 - 3y - 12y^2 + 10y = 9y - 24 - 8y$ $7y = y - 24$ $6y = -24$ $y = -4$ г) $15x + 6x(2-3x) = 9x(5-2x) - 36$ $15x + 12x - 18x^2 = 45x - 18x^2 - 36$ $27x = 45x - 36$ $-18x = -36$ $x = 2$