(1)
Differentiating both sides of equation (1) with respect to x, successively, we get
dy
dx  = – a sinx + b cosx
2
d y2
dx
 = – a cos x – b sinx
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DIFFERENTIAL EQUATIONS
385
Substituting the values of 
2
d y2
dx
 and y in the given differential equation, we get
L H S = (– a cos x – b sin x) + (a cos x + b sin x) = 0 = R