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Find three linearly independent solutions (see Problem 35) of the given third-order differential equation and write a general solution as an arbitrary linear combination of it. z'''+2z''-4z'-8z=0

Short Answer

Expert verified

z(t)=c1e-2t+c2te-2t+c3e2tis the solution of the given equationz'''+2z''-4z'-8z=0

Step by step solution

01

Differentiate the value of z

Given differential equation isz'''+2z''-4z'-8z=0

Letz=ert, thenz'(t)=rert and

z''(t)=r2ertz'''=r3ert

Then the auxiliary equation isr3ert+2r2ert-4rert-8ert=0

r3+2r2-4r-8ert=0r3+2r2-4r-8=0

02

Substitute the value for r

Let substitute r=1

13+2(1)2-4-8≠0

Now substituter=2

23+2(2)2-4(2)-8=0

Therefore r=2 is the solution of the auxiliary equation r3+2r2-4r-8=(r-2)r2+4r+4

(r-2)r2+4r+4=0

Therefore, the solutions are r=2and (r+2)2=0

r=-2,-2,2z(t)=c1e-2t+c2te-2t+c3e2t

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