1)0,64х^2+1,6+1=0 2)-0,5х^2+6x-7=0 3)3x^2-x-2=0 4) -5x^2+2x-2.5=0

1. 0,64х^2 + 1,6х + 1 = 0;

64x^2 + 160x + 100 = 0;

16x^2 + 40x + 25 = 0;

D = 40^2 - 4 * 16 * 25 = 1600 - 1600 = 0;

x = - 40/32 = - 5/4.

2. - 0,5x^2 +6x -  7 = 0;

5x^2 - 60x + 70 = 0;

x^2 - 12x + 14 = 0;

D = 144 - 56 = 88;

x = (12 +- sqrt88)/ 2;

x1 = 6 + 2sqrt22;

x2 = 6 -  2sqrt22. 

3. 3x^2 -  x -  2 = 0;

D = 1 + 14 = 15;

x = (1 +- sqrt15)/6.

4. - 5x^2 + 2x -  2,5 = 0;

50x^2 + 20x - 25 = 0;

10x^2 + 4x -  5 = 0;

D = 16 + 200 = 216;

x = (-4 +- sqrt216)/ 20.