Объяснение:

1)x^2-6x+5=0

D=36-20=16

x1=(6+4)/2=5

x2=(6-4)/2=1

2)3x^2-8x+5=0

D=64-4•3•5=4

x1=(8+2)/6=10/6=5/3

x2=(8-2)/6=1

3)4x^2-10x-6=0

D=100-4•4•(-6)=196

x1=(10+14)/8=3

x2=(10-14)/8=-1/2

4)5x^2+4x-12=0

D=16-4•5•(-12)=256

x1=(-4+16)/10=12/10=6/5

x2=(-4-16)/10=-2

5)x^2+2sqrt(5)x-20=0

D=20-4•(-20)=100

x1=(-2sqrt(5)+10)/2=-2sqrt(5)+5

x2=(-2sqrt(5)-10)/2=-2sqrt(5)-5

sqrt-корень