1) x²-10x+16=0 2) x²+14x+45=0 3) x²-x-42=0 4) x²+7.3x+2.1=0

1) Выделяем квадрат разности двух чисел:

x^2 - 10 * x + 16 = x^2 - 2 * x * 5 + 25 - 9 = (x - 5) ^2 - 9.

(x - 5) ^2 - 9 = 0;

(x - 5) ^2 = 9;

x - 5 = - 3;

x = 2;

x - 5 = 3;

x = 8;

Корни - x = 2, x = 8.

2) x^2 + 14 * x + 45 = 0;

Ищем дискриминант:

D = 14^2 - 4 * 45 = 196 - 180 = 16;

x1 = (-14 - 4) / 2 = - 9;

x2 = (-14 + 4) / 2 = - 5.

3) x^2 - x - 42 = 0;

Ищем дискриминант:

D = 1 + 4 * 42 = 169;

x1 = (1 - 13) / 2 = - 6;

x2 = (1 + 13) / 2 = 7.

4) x^2 + 7,3 * x + 2,1 = 0;

10 * x^2 + 73 * x + 21 = 0;

D = 73^2 - 210 * 4 = 4489;

x1 = (-73 - 67) / 20 = - 7;

x2 = (-73 + 67) / 20 = - 0,3.