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Q21E

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Fundamentals Of Differential Equations And Boundary Value Problems
Found in: Page 180
Fundamentals Of Differential Equations And Boundary Value Problems

Fundamentals Of Differential Equations And Boundary Value Problems

Book edition 9th
Author(s) R. Kent Nagle, Edward B. Saff, Arthur David Snider
Pages 616 pages
ISBN 9780321977069

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Short Answer

Find a particular solution to the differential equation.

x''(t)-4x'(t)+4x(t)=te2t

The particular solution is xp=16t3e2t.

See the step by step solution

Step by Step Solution

Step 1: Firstly, write the auxiliary equation of the above differential equation 

Consider the given differential equation,

x''(t)-4x'(t)+4x(t)=te2t                       (1)

Write the homogeneous differential equation of the equation (1),

x''(t)-4x'(t)+4x(t)=0

The auxiliary equation for the above equation,

m2-4m+4=0

Step 2: Now find the roots of the auxiliary equation

Solve the auxiliary equation,

m2-4m+4=0(m-2)2=0

The roots of the auxiliary equation are;

m1=2,   &   m2=2

The complementary solution of the given equation is;

xc=c1e2t+c2te2t

Step 2: Find a particular solution.

Therefore, the particular solution of equation (1),

xp=t2(At+B)e2t                           (2)

Now find the derivative of the above equation,

xp'(t)=(3At2+2Bt)e2t+2t2(At+B)e2txp'(t)=(3At2+2Bt+2At3+2t2B)e2txp''(t)=(12At2+8Bt+6At+4At3+4t2B+2B)e2t

From the equation (1), substitute the value of xp''(t),  xp'(t) and xp(t), we get

x''p(t)-4xp'(t)+4xp(t)=te2t(12At2+8Bt+6At+4At3+4t2B+2B)e2t-4(3At2+2Bt+2At3+2t2B)e2t+4t2(At+B)e2t=te2tte2t(6A)+2Be2t=te2t

Step 4: Final conclusion. 

Comparing all coefficients of the above equation,

6A=1  A=16B=0

Therefore, the particular solution of equation (1),

xp=t2(At+B)e2txp=t2(t+0)e2txp=t3e2t

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