- #1
John O' Meara
- 330
- 0
Integrate cosh(4z) w.r.t., z, for any path from [tex] \frac{-\pi i}{8} \inbox{to } \frac{\pi i}{8} [/tex]. If the function is analytic, i.e., obeys Cauchy - Riemann equations we can integrate as in standard calculus.
[tex] \frac{{\partial \cosh(4(x+iy)}}{{\partial x}} = a\sinh(4x + 4iy) \\ \frac{{\partial \cosh(4x +4iy)}}{{\partial y }} = 4i\sinh(4x + 4iy)\\[/tex]. Therefore [tex] u_x [/tex] and [tex] v_y [/tex] are not equal, therefore the cosh(4z) is not analytic. So we integrate as follows: C (the path of integration) can be represented by z(t)= 0 + it, [tex] \frac{-\pi}{8} \leq t \leq \frac{\pi}{8}\\[/tex] Hence [tex] \dot z(t) = \iota \\[/tex] and f(z(t)) = cosh(it), therefore [tex] \int_C \cosh(z) dz = \int_{\frac{-\pi}{8}}^\frac{\pi}{8} \cosh(it)\iota dt \\[/tex] = sinh(it) evulated at the respective limits = [tex] 2\sinh(\frac{\iota\pi}{8}) \ [/tex]
I don't think that this is correct, I think my Z(t) = 0 +it is wrong.
[tex] \frac{{\partial \cosh(4(x+iy)}}{{\partial x}} = a\sinh(4x + 4iy) \\ \frac{{\partial \cosh(4x +4iy)}}{{\partial y }} = 4i\sinh(4x + 4iy)\\[/tex]. Therefore [tex] u_x [/tex] and [tex] v_y [/tex] are not equal, therefore the cosh(4z) is not analytic. So we integrate as follows: C (the path of integration) can be represented by z(t)= 0 + it, [tex] \frac{-\pi}{8} \leq t \leq \frac{\pi}{8}\\[/tex] Hence [tex] \dot z(t) = \iota \\[/tex] and f(z(t)) = cosh(it), therefore [tex] \int_C \cosh(z) dz = \int_{\frac{-\pi}{8}}^\frac{\pi}{8} \cosh(it)\iota dt \\[/tex] = sinh(it) evulated at the respective limits = [tex] 2\sinh(\frac{\iota\pi}{8}) \ [/tex]
I don't think that this is correct, I think my Z(t) = 0 +it is wrong.
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