Helpp! derivative and equation of the tangent line √x/x at (4, 1/2)?

so i got the derivative to be -1/2x^-2/3 and i know thats right but when i plug 4 into it i get a humongous number (-99/500) and that would be the slope then, i get what to do next (point-slope form equation) but i just wanted to make sure the slop is correct for the point (4, 1/2)...please help! i have it all worked out, i just need to make sure, thanks! (: