Its more a simplifying problem... I was trying to differentiate this using definition principal 1-x^1/2 But I got stuck here : (1-(x+h)^1/2 - (1-x^1/2))/h I mean how do you explan something to the power of half or infact any fraction? I know I can change it to 1/sqrt(x+h)... but it just makes things more complicated... coz I can't get rid of the h then... But using power rule is simple... 1-x^1/2 = -1/2X^-1/2 On top of that, I want to ask... are the constant numbers ignorable in differentiation? For example 4 - x^2 is -2x, I can just apply power rule on -x^2 and get the same answer... If I were to differentiate this by definition, can I just do -x^2 and ignore 4 too?