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Engineering Mathematics Miscellaneous

Engineering Mathematics

  1. The value of the integral
    -∞
    sin x
    dx is
    x² + 2x + 2

    evaluated using contour integration and the residue theorem is
    1. πsin (1)
      e
    2. - πcos (1)
      e
    3. sin (1)
      e
    4. cos (1)
      e
Correct Option: A

I = -∞
sin (x)
x² + 2x + 2

let f(x) =
Im(eix)
z² + 2z + 2

Then poles of f(z) are given by z² + 2z + 2 = 0
∴ z = – 1 ± i
R1 = Res: (f(z): z = -1 + i)
Ltz→-1±1[z-(-1+i)]
eix
[z-(-1+1)][z-(-1-i)]

=
ei(-1+i)
=
e-i-1
-1 + i + 1 + i2i


= IM[πe-1(cos(1) - isin(1))] = -
π sin(1)
e



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