1) Д = -4^2 -4*1*3 = 4
x1 = 1
x2 = 3
2) x(x+9) = 0
x= 0 x+9 = 0
x = -9
3) D = -1^2 -(-4)*7*8 = 225
x1 = -1
x2 = 8/7
4) 2x^2 = 50
x^2 = 50/2
x^2 = 25
x1 = 5 x2 = -5
5) x^2 =36
x1 = 6 x2 = -6
6) 0.3x(3 - 10x) = 0
0.3 x =0 3-10x =0
x = 0 10x = 3
x = 3/10 = 0.3
6) 2x²-57+2=0
2x^2 -55 = 0
2x^2 = 55
x^2 = 55/2
x^2 = 27.5
x = корень 27,5
7) x²-2x-6=0
D = -2^2 -4*(-4)*1*6 =28
x1 = (2 + кореннь28) /2
х2 = (2-корень28)/2