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Engineering Mathematics Miscellaneous

Engineering Mathematics

  1. A differential equation is given as
    x2
    d2y
    - 2x
    dy
    + 2y = 4
    dx2dx

    The solution of the differential equation in terms of arbitrary constants C1 and C2 is
    1. y = C1 x2 + C2 x + 4
    2. y =
      C1
      + C2x + 2
      x2
    3. y = C1 x2 + C2 x + 2
    4. y =
      C1
      + C2x + 4
      x2
Correct Option: C

x2 =
d2y
- 2x
dy
+ 2y = 4
dx2d

Let x = ez
CF :
d2y
= θ(θ - 1)
dx2

⇒ θ(θ - 1) - 2θ + 2 = 0
⇒ θ2 - 3θ + 2 = 0
(θ - 1)(θ - 2) = 0
θ = 1,2
θ = C1ez + C1e2z
y = C1x2 + C2x
PI : -
4
+
4
(θ - 1)(θ - 2)

= + 4(1 -θ)-1 -
4
1 -
θ
-1
22

= + 4(1 - θ + ...) - 21 +
θ
+ .....
2

= + 4 – 2 = 2 (Neglecting higher order term)
y = CF + PI
y = C1 x2 C2 x + 2



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