Solve dt2d2y(t)−4dtdy(t)+4y(t)=64sin(2t), such that y(0)=0 and y′(0)=1:The general solution will be the sum of the complementary solution and particular solution. Find the complementary solution by solving dt2d2y(t)−4dtdy(t)+4y(t)=0:Assume a solution will be proportional to eλt for some constant λ.Substitute y(t)=eλt into the differential equation:dt2d2(ext)−4dtd(ext)+4eλt=0Substitute dt2d2(eλt)=λ2eλt and dtd(eλt)=λeλtλ2eλt−4λeλt+4eλt=0Factor out eλt(λ2−4λ+4)eλt=0Since eλt=0for any finite λ, the zeros must come from the polynomial:λ2−4λ+4=0
Factor:(λ−2)2=0Solve for λ:λ=2 or λ=2The multiplicity of the root λ=2 is 2 which gives y1(t)=c1e2t,y2(t)=c2e2tt as solutions, where c1 and c2 are arbitrary constants.The general solution is the sum of the above solutions:y(t)=y1(t)+y2(t)=c1e2t+c2e2ttDetermine the particular solution to dt2d2y(t)−4dtdy(t)+4y(t)=64sin(2t) by the method of undetermined coefficients:The particular solution to dt2d2y(t)−4dtdy(t)+4y(t)=64sin(2t) is of the form: yp(t)=a1cos(2t)+a2sin(2t)Solve for the unknown constants a1 and a2:Compute dtdyp(t):dtdyp(t)=dtd(a1cos(2t)+a2sin(2t))=−2a1sin(2t)+2a2cos(2t)
Compute dt2d2yp(t):dt2d2yp(t)=dt2d2(a1cos(2t)+a2sin(2t))=−4a1cos(2t)−4a2sin(2t)Substitute the particular solution yp(t) into the differential equation:dt2d2yp(t)−4dtdyp(t)+4yp(t)=64sin(2t)−4a1cos(2t)−4a2sin(2t)−4(−2a1sin(2t)+2a2cos(2t))+4(a1cos(2t)+a2sin(2t))=64sin(2t) Simplify:−8a2cos(2t)+8a1sin(2t)=64sin(2t)Equate the coefficients of cos(2t) on both sides of the equation:−8a2=0Equate the coefficients of sin(2t) on both sides of the equation:8a1=64Solve the system:a1=8a2=0
Substitute a1 and a2 intoyp(t)=cos(2t)a1+sin(2t)a2:yp(t)=8cos(2t) The general solution is: y(t)=yc(t)+yp(t)=8cos(2t)+c1e2t+c2e2tt Solve for the unknown constants using the initial conditions: Compute dtdy(t):dtdy(t)=dtd(8cos(2t)+c1e2t+c2e2tt)=−16sin(2t)+2c1e2t+c2e2t+2c2e2tt Substitute y(0)=0 into y(t)=8cos(2t)+e2tc1+e2ttc2:c1+8=0Substitute y′(0)=1 into dtdy(t)=−16sin(2t)+2e2tc1+e2tc2+2e2ttc2:2c1+c2=1 Solve the system:c1=−8c2=17Substitute c1=−8 and c2=17 into y(t)=8cos(2t)+e2tc1+e2ttc2 Answer:y(t)=8cos(2t)+e2t(17t−8)
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