Найдите корень уравнения:
а) 3x(2x - 1) - 6x(7 + х) = 90;
б) 1,5x(3 + 2х) = 3х(х + 1) - 30;
в) 5x(12x - 7) - 4х(15x - 11) = 30 + 29x;
г) 24x - 6x(13x - 9) = -13 - 13x(6x - 1).

Решение:


a) 3x • (2x - 1) - 6x • (7 + х) = 90 => 6x2 - 3x - 42x - 6x2 = 90 => -45x - 90 => x = -2;
б) 1,5x • (3 + 2х) = 3х • (х + 1) - 30 => 4,5x + Зх2 = 3х2 + 3х - 30 => 4,5х - 3х + 3х2 - 3х2 = -30 => 1,5х =
= -30 => х = -20;
в) 5x • (12x - 7) - 4х • (15x - 11) = 30 + 29x => 60х2 - 35х - 60х2 + 44х = 30 + 29х => -35х + 44х - 29х =
= 30 => -20х = 30 => х = -1,5;
г) 24x - 6x • (13x - 9) = -13 - 13x • (6x - 1) => 24х - 78х2 + 54х = -13 - 78х2 + 13х => 24х + 54х - 13х - - 78х2 + 78х2 = =-13 => 65х = -13 => х = -0,2.