x1²+x2²
=x1²+2x1x2+x2²-2x1x2
=(x1+x2)²-2x1x2
|x1-x2|
=√(x1-x2)²
=√(x1²-2x1x2+x2²)
=√(x1²+2x1x2+x2²-4x1x2)
=√[x1+x2)²-4x1x2]
x1³+x2³
=(x1+x2)(x1²-x1x2+x2²)
=(x1+x2)[(x1+x2)²-2x1x2-x1x2]
=(x1+x2)[(x1+x2)²-3x1x2]