given that y=1nx/x, x>0
(a) find the value of x for which dy/dx=0
(b) find the value of x for y=0
(c) find the point where d^2y/dx^2=0
y = lnx/x
y' = ((1/x)x - lnx)/x^2
= (1-lnx)/x^2
y'=0 when lnx = 1, or x=e
y=0 when lnx=0, or x=1
y" = (2lnx-3)/x^3
y" = 0 when 2lnx = 3, or x=e^(3/2) or e√e