Find the complete solution of y" - 2y' + 2y

fumefluosault7pa

fumefluosault7pa

Answered question

2022-02-14

Find the complete solution of y" - 2y' + 2y = sin2x + e* cos x .

Answer & Explanation

bijteny85

bijteny85

Beginner2022-02-15Added 10 answers

Solve (d2y(x))/(dx2)2(dy(x))/(dx)+2y(x)=ecos(x)+sin(2x):The general solution will be the sum of the complementary solution and particular solution.Find the complementary solution by solving (d2y(x))/(dx2)2(dy(x))/(dx)+2y(x)=0:Assume a solution will be proportional to e(λx) for some constant λ.Substitute y(x)=e(λx) into the differential equation:(d2)/(dx2)(e(λx))2d/(dx)(e(λx))+2e(λx)=0Substitute (d2)/(dx2)(e(λx))=λ2e(λx) and d/(dx)(e(λx))=λe(λx):λ2e(λx)2λe(λx)+2e(λx)=0Factor out e(λx):(λ22λ+2)e(λx)=0

since e(λx)!=0 for any finite λ, the zeros must come from the polynomial:λ22λ+2=0Solve for λ:λ=1+i or λ=1iThe roots λ=1±i give y1(x)=c1e((1+i)x),y2(x)=c2e((1i)x) as solutions, where c1 and c2 are arbitrary constants.The general solution is the sum of the above solutions:y(x)=y1(x)+y2(x)=c1e((1+i)x)+c2e((1i)x)Apply Euler's identity e(α+iβ)=eαcos(β)+ieαsin(β):y(x)=c1(excos(x)+iexsin(x))+c2(excos(x)iexsin(x))Regroup terms:y(x)=(c1+c2)excos(x)+i(c1c2)exsin(x)Redefine c1+c2 as c1 and i(c1c2) as c2

since these are arbitrary constants:y(x)=c1excos(x)+c2exsin(x)Determine the particular solution to (d2y(x))/(dx2)2(dy(x))/(dx)+2y(x)=ecos(x)+sin(2x) by the method of undetermined coefficients:The particular solution will be the sum of the particular solutions to

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