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082-Engineering-Mathematics-Anthony-Croft-Robert-Davison-Martin-Hargreaves-James-Flint-Edisi-5-2017

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602 Chapter 19 Ordinary differential equations I

5 Find the general solution ofy ′′ +16y =x 2 .

6 Find the particular solution of

y ′′ +3y ′ −4y =e x ,y(0) =2,y ′ (0) =0.

7 Aparticle moves in astraightline such that its

displacement from the origin Oisx,wherexsatisfies

the differentialequation

d 2 x

dt 2 +16x=0

(a) Findthe general solution ofthisequation.

( ) ( )

π

π

(b) Ifx = −12, andẋ = 20,findthe

4 4

displacement ofthe particlewhent = π 2 .

8 Usean integrating factorto solvethe differential

equation

dx

+xcott =cos3t

dt

Solutions

1 (a) x=Ae 2t

(b) x=3ln|1+t|+c

1

(c) y=

A−sinx

2 y=2x+3

3 x=t+ c t

4 x = e2t (4cost +sint)

17

+ce −2t

5 y=Acos4x+Bsin4x+ x2

16 − 1

128

6 y = 39ex +11e −4x

25

+ xex

5

7 (a) Asin4t +Bcos4t (b) 12

cos2t − 1

8 sint;x(t) =

2 cos4t+c

4sint

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