Because the two roots are different, so: a≠0, b? -4ac>0 .
Axe? +bx+c=0
x? +(b/a)x+c/a=0
x? +2[b/(2a)]x+[b/(2a)]? -[b/(2a)]? +c/a=0
x? +2[b/(2a)]x+[b/(2a)]? =[b/(2a)]? -c/a
[x+b/(2a)]? =b? /(4a? )-4ac/(4a? )
[x+b/(2a)]? =(b? -4ac)/(4a? )
x+b/(2a)= √[(b? -4ac)/(4a? )]
x+b/(2a)= [√(b? -4ac)]/(2a)
x=-b/(2a) [√(b? -4ac)]/(2a)
x=[-b √(b? -4ac)]/(2a)
x 1=[-b+√(b? -4ac)]/(2a)、x2=-[b+√(b? -4ac)]/(2a)