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Engineering Mathematics Miscellaneous

Engineering Mathematics

  1. For the equation
    dy
    + 7x2y = 0 , if y(0) = 3 / 7 ,
    dx

    then the value of y(1) is
    1. 3
      e-7 / 3
      7

    2. 3
      e-3 / 7
      7

    3. 7
      e-3 / 7
      3

    4. 7
      e-7 / 3
      3
Correct Option: A

From question, we have

dy
+ 7x2y = 0 , y(0) =
3
, y(1) = ?
dx7

dy
= -7x2y
dx

dy
= -7x2dx
y

ln y = -
7x3
+ C
3

y = e{ (-7x3 / 3) + C}
y(0) = eC =
3
7

C = ln
3
7

ln y = -
7x3
+ ln
3
37

ln y - ln
3
= -
7x3
73

ln
7y
= -
7x3
33

y =
3
e (-7x3/ 3)
7

∴ y(1) =
3
e (-7/ 3)
7



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