Find the general solution of the differential equation d^2y/dx^2 - 5*dy/dx + 4y = 2x

Solve complimentary function: Let y = emx then,
d2y/dx2 - 5dy/dx + 4y = 0
m2emx - 5memx + 4emx = 0 (substituting for y)
emx(m2 - 5m + 4) = 0
emx(m - 4)(m - 1) = 0
Therefore m=4 and m=1, so the c.f. is y = Ae4x + Bex where A,B are constants

Solve particular integral: Let y = ax + b and substitute into the differential equation
0 - 5a + 4(ax + b) = 2x
4ax + (4b - 5a) = 2x
Therefore 4a=2 and 4b-5a=0 so a=1/2, b =5/8

Hence the general solution is y = c.f + p.i =  Ae4x + Bex + 1/2 x + 5/8

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Answered by Peter M. Further Mathematics tutor

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