Doubt in method of Undetermined Coefficients $(D^3+3D^2+2D)y=x^2$.

ordinary differential equations

Solve $(D^3+3D^2+2D)y=x^2, D \equiv \dfrac{d}{dx}$

Choosing, trial solution as $y=a_0+a_1x+a_2x^2$

If i substitute this in given differential equation,

$0+3(2a_2)+2(a_1+2a_2x)=x^2 $

Comparing corresponding coefficients, i get,

$a_0=0=a_1 = a_2$ –> it seems i made wrong some where, Pls correct me.

Best Answer

Hint: Try with $y_p=A+B x+C x^2+D x^3$ then $$(D^3+3D^2+2D)y=(2 B + 6 C + 6 D)+ (4 C + 18 D)x+ 6 Dx^2\equiv x^2$$

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