Non-Homogeneous Linear Differential Equations (Methods for finding PI for sin(ax) ,cos(ax), x^m)
The particula...
Question
The particular solution for the differential equaiton d2ydx2+3dydx+2y=5cosx is
A
0.5cosx+1.5sinx
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B
1.5cosx+0.5sinx
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C
1.5sinx
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D
0.5cosx
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Solution
The correct option is A0.5cosx+1.5sinx Given DE is d2ydx2+3dydx+2y=5cosx P.I=1(D2+3D+2).5cosx
Using =1f(D2)cos(ax+b)=1f(−a2)cos(ax+b) =P.I=51(−12)+3D+2cosx =5(3D+1)cosx =5×3D−19D2−1cosx =5×3D−19(−1)−1cosx =5−10×(3D−1)cosx P.I=−12×(3D−1)cosx =−12×[(3(−sinx)−cosx] P.I=1.5sinx+0.5cosx