find derivative using limit definition:

Question

f(x) = x - sqrt(x)

so f'(x) = lim
h->0 [f(x+h) - f(x)]/h

but I keep trying to solve by multiplying by the conjugate but I can't figure it out..there's nothing that can be cancelled or anything and I can't get the derivative

Answer 1

Some studies suggest that kidney mass K in mammals (in kilograms) is related to body mass m (in kilograms) by the approximate formula K = .007m^(0.85). Calculate dK/dm at m = 68. Then calculate the derivative with respect to m of the relative kidney-to-mass ratio K/m at m = 68.

Answer 2

ahh sorry that was supposed to be a new question. i need help with both though hahah, so pleaseee help me! i know derivatives but not in these contexts.