Substitute u = ah, rewrite to a × (standard def of derivative with u -> 0)? Lim h -> 0 implies u-> 0 (easily prooven using epsilon delta), so I think that should suffice?
Substitute u = ah, rewrite to a × (standard def of derivative with u -> 0)? Lim h -> 0 implies u-> 0 (easily prooven using epsilon delta), so I think that should suffice?