Unless otherwise provided in:
(a) Chapters 1 through 20 of this Title;
(b) the articles of incorporation; or
(c) an agreement unanimously approved by the shareholders and disclosed in the articles of incorporation and on the corporation's share certificates,
all corporate powers must be exercised by or under the authority of, and the business and affairs of a corporation must be managed under the direction of, a board of directors. If the authority of the board is dispensed with or limited by a provision in the articles of incorporation under (b) or by a shareholder agreement under (c), the articles or the agreement shall describe who is to perform some or all of the duties of a board of directors.