42 решите пжпжпж дам банкеты

1) (x-2,5) = 45
x - 5x + 6,25 = 45
x - 5x - 38,75 = 0
a=1, b=-5, c=-38,75
D = b - 4ac = (-5) - 4*1*(-38,75) = 25 + 155 = 180 gt; 0
x1 = -b + D/2a = 5 + 180/2;  
x2 = -b - D/2a = 5 - 180/2;

 Ответ :  5+180/2; 5 -180/2;  

4) (5x+1) = 400
25x + 10x + 1 = 400
25x + 10x - 399 = 0
a1=25, b=10, c=-399
k = b/2 = 10/2 = 5;
D1 = k - ac= 5 - 25*(-399) = 25 + 9975 = 10000 = 100 gt; 0
D1 gt; 0
x1 = -k + D1/a = -5 + 100/25 = 95/25 = 3,8;
x2 = -k + D1/a = -5 - 100/25 = -105/25 = 4,2;

 Ответ : 3,8; 4,2;

2) (3-2x) = 0,04;
9 - 12x + 4x = 0,04;
4x - 12x + 9 - 0,04 = 0
4x - 12x + 8,96 = 0
a=4, b=-12, c=8,96
k = b/2 = -12/2 = -6
D1 = k - ac = (-6) - 4*8,96 = 36 - 35,84 = 0,16 = (0,4) gt; 0
D1 gt; 0
x1 = -k+D1/a = 6+0,4/4 = 6,4/4 = 1,6;
x2 = -k-D1/a = 6-0,4/4 = 5,6/4 = 1,4;

 Ответ : 1,6; 1,4;