а)6x-x=0, б)-9+4x=0, в)12x+7x+1=0, г)3x+5x+6=0

   а)

• 6x^2 - x = 0;
• x(6x - 1) = 0;

• [x = 0;
  [6x - 1 = 0;
• [x = 0;
  [6x = 1;
• [x = 0;
  [x = 1/6.

   б)

• -9 + 4x^2 = 0;
• (2x)^2 - 3^2 = 0;
• (2x + 3)(2x - 3) = 0;

• [2x + 3 = 0;
  [2x - 3 = 0;
• [2x = -3;
  [2x = 3;
• [x = -3/2;
  [x = 3/2;
• [x = -1,5;
  [x = 1,5.

   в)

• 12x^2 + 7x + 1 = 0;
• D = 7^2 - 4 * 12 * 1 = 49 - 48 = 1;
• x = (-7 1)/(2 * 12) = (-7 1)/24;
• x1 = (-7 - 1)/24 = -8/24 = -1/3;
• x2 = (-7 + 1)/24 = -6/24 = -1/4;

   г)

• 3x^2 + 5x + 6 = 0;
• D = 5^2 - 4 * 3 * 6 = 25 - 72 = -47 lt; 0 - нет решений.

   Ответ: а) 0; 1/6; б) -1,5; 1,5; в) -1/3; -1/4; г) нет решений.