练习129 1.求下列各微分方程的通解 (1)2y"+y-y=2e; (2)y"+ay=e; (3)2y"+5y=5x2-2x-1; (4y"+3y+2y=3re; (5)y-2y' +5y=e sin2 (7)"+5y+4y=3-2x;练习 12-9