1) x^2-6x+8=0
D= 36-4*8 = 36-32 = 4
x1= (6-2)/2 = 4/2= 2
х2= (6+2)/2 = 8/2 =4
2) 7x^2-9x+2=0
D= 81- 4*7*2= 81-56 = 25
x1= (9-5)/2 = 4/2 =2
х2= (9+5)/2 =14/2 = 7
3)x^2+20x+91=0
D= 400- 4*91 =400- 364 = 36
x1= (-20-6)/2 = -26/2 = -13
х2= (-20+6)/2 = -14/2 = -7
4) 7x^2-8x+1=0
D= 64-4*7*1= 64-28 = 36
x1= (8-6)/2 = 2/2 = 1
х2= (8+6)/2 = 14/2 = 7
5)3x^2+7x=0
x(3x+7)=0
x=0 или 3х+7=0
х= -2 1/3
6)4x^2-1=0
4x^2= 1
x^2= 1/4
х= 1/2
7)x^2-x=0
x(x-x)=0
x=0 или х-х=0
2х=0
х=0
8)x^2=-5x-6
x^2+5x+6=0
D= 25- 4*6= 25-24= 1
x1=(-5-1)/2 = -6/2 = -3
х2=(-5+1)/2= -4/2 = -2
9) не оч врубилась)
10) x^2+12=7x
x^2+12-7x=0
D= 144-4*(-7)= 144+28= 172
х1= (12-2√43)/2 = 2(6-√43)/2 =6-√43
х2= (12+2√43)/2 = 6+√43