1. Find the general solution of the given higher-order differential equation.
d^3u/ dt^3 + d^2u/ dt^2 − 2u = 0
u(t) = ____
2. Find the general solution of the given higher-order differential equation.
y''' − 9y'' + 15y' + 25y = 0
y(x) =____
1
Expert's answer
2020-06-28T17:16:19-0400
u′′′+u′′−2u=0 Alinear homogeneous equation The general solution isu(t)=uhr3+r2−2=0⟹p=±2,±1,q=±1qp=±1,±2,.....f(1)=0→1 is a root of the equation Divider3+r2−2 byr−1 we get r2+2r+2Use quadratic Formula →r=−1+i,r=−1−i,r=1∴u(t)=c1et+e−t(c2cost+c3sint)(1)y′′′−9y′′+15y′+25y=0 Alinear homogeneous equation The general solution is y(x)=yhr3−9r2+15r+25=0⟹p=±5,±1,±25,q=±1qp=±1,±5,....f(−1)=0→1 is a root of the equation Divider3−9r2+15r+25 byr+1 we get r2−10r+25r2−10r+25=(r−5)(r−5)→r=5,r=5,r=−1∴y(x)=c1e−x+c2e5x+c3xe5x(2)
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