x1^2/x1x2+x2^2/x1x2-2x1x2/x1`x2=(x1^2+x2^2-2x1x2)/x1x2=[(x1+x2)^2]/x1x2
x1/x2 +x2/x1 -2=(x1²+x2²-2x1x2)/x1x2=(x1+x2)²/x1x2