Solving 00 0 Without Characteristic Equations
quation Solve: \[ y'' + y = \tan x \] The homogeneous equation \( y'' + y = 0 \) has solutions: \[ y_1 = \cos x, \quad y_2 = \sin x \] Applying variation of parameters, one constructs \( u_1 \) and \( u_2 \) from the