A resolution in writing signed by all the directors entitled to receive notice of a meeting of directors or (as the case may be) a committee of directors duly convened and held may consist of several documents in the like form each signed by one or more directors; but a resolution signed by an alternate director need not also be signed by his appointor and, if it is signed by a director who has appointed an alternate director, it need not be signed by the alternate director in that capacity.