f(x)=(x^2 2x 1/2)/x
x∈[1,∝)
f`(x)=[(2x 2)x-(x^2 2x 1/2)]/x^2
=(2x^2 2x-x^2-2x-1/2)/x^2
=(x^2-1/2)/x^2
f`(x)