1) x²+4 х-212) 12x²-7 х+13) x²-2 ч-1

1) x^2 + 4x - 21 = 0.

Корни квадратного уравнения вида ax^2 + bx + c = 0 определяются

по формуле: x12 = (-b + - √ (b^2 - 4 * a * c) / 2 * a.

x12 = (-4 + - √ (16 - 4 * 1 * (-21)) / 2 * 1 = (-4 + - 10) / 2;

x1 = (-4 - 10) / 2 = - 7; x2 = (-4 + 10) / 2 = 3.

2) 12x^2 - 7x + 1 = 0.

x12 = (7 + - √ (49 - 4 * 12 * 1) / 2 * 12 = (7 + - 1) / 2 * 12;

x1 = (7 - 1) / 12 = 1/2; (7 + 1) / 12 = 2/3.

3) x^2 - 2x - 1 = 0.

x12 = (2 + - √ (4 - 4 * 1 * (-1)) / 2 * 1 = (2 + - √8) / 2;

x1 = (2 - √8) / 2 = 1 - √2; x2 = (2 + √8) / 2 = 1 + √2.