x-√(x²-x)=【x-√(x²-x)】【x+√(x²-x)】/【x+√(x²-x)】=(x²-x²+x)/【x+√(x²-x)】=x/【x+√(x²-x)】=1/【1+√(1-1/x)】=1/(1+1)=1/2
