x1=[-b-√(b²-4ac)]/2a
x2=[-b+√(b²-4ac)]/2a
所以
x1+x2=[-b-√(b²-4ac-b+√(b²-4ac)]/2a
=-2b/2a
=-b/a
x1x2
=[-b-√(b²-4ac)][-b+√(b²-4ac)]/(4a²)
分子平方差
=[b²-(b²-4ac)]/4a²
=4ac/4a²
=c/a
x1=[-b-√(b²-4ac)]/2a
x2=[-b+√(b²-4ac)]/2a
所以
x1+x2=[-b-√(b²-4ac-b+√(b²-4ac)]/2a
=-2b/2a
=-b/a
x1x2
=[-b-√(b²-4ac)][-b+√(b²-4ac)]/(4a²)
分子平方差
=[b²-(b²-4ac)]/4a²
=4ac/4a²
=c/a