1) 7 х²-16 х+8=0

2) х²-16 х+56=0

3) 2 х²-21 х-23=0

1) 7x-16x+8=0

a=7, b=16, c=8

D=-b²-4ac=16²-4•7•8=256-224=32

x½ = (-b±√D) 2a = (-16±√32) : 14=

x¹ = - (16-6) : 14=-22:14=-1,5,

x² = (-16+6) : 14=-10:14=-0,7

2) x²-16x+56=0

a=1 b=16. c=56

D (дискриминант) = b²-4ac=16²-4•1•56=256-224=32

x½ = (-16 ±√32) : 2=

x¹ = (-16-6) : 2=-22:2=-11

x² = (-16+6) : 2=-10:2-5

3) 2x²-21-23=0

a=2. b = (-21.) c = (-23)

D=b²-4ac=-21²-4•2•23=441-184=257

x½ = (-b±√D) : 2a = (-21±16) : 4

x¹ = (-21-16) : 4=9,25

x² = (-21+16) : 4=-1,25