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I'm having the integral of a function over path C1 and C2 .I want to have both c1 and c2 on the left side of my page but anything I use doesn't work . I tried to put it with the align* , itemize , [], and many other things , but the result was always the same . what should I do to put them on the left side of the page ?


‎ ‎‎
‎C_1:  x= y‎ ‎\implies ‎z(t) =‎ ‎x(t)+ ‎iy(t)= ‎(1+i)t ‎‎\qquad 0 ‎‎‎‎\leqslant t ‎‎‎‎\leqslant ‎1‎‎ ‎‎\\
f[z(t)] = Re z(t) = t, ‎\quad ‎dz =‎ ‎(1+i)dt ‎ ‎‎\\‎
\int ‎Re z‎ ‎dz  =‎‎ ‎(1+i) ‎\int_‎{0}^{1} t‎ ‎dt = ‎‎‎‎\frac{1}{2}(1+i)‎‎ \\‎‎[1cm]‎
C_2:  ‎‎z(t)  =‎‎ ‎‎
‎\left\{\!\! \begin{array}{l}‎
t ‎‎‎‎\qquad  ‎‎0‎ \leqslant t \leqslant 1‎‎ ‎‎\\‎‎‎
1+i(t-1) ‎‎\qquad‎‎ a \leqslant 1 \leqslant 2‎
‎\end{array}\right‎. ‎ ‎‎\\‎
\int_{c_2} Rez dz = \int_{0}^{1} t dt  + i \int_{1}^{2}  dt = ‎\frac{1}{2} +‎ i‎ ‎‎


enter image description here

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If you use align* or a related environment of amsmath, use & as alignment marker. Usually this is done right before a relation symbol, for aligning at the relation symbol.

In some amsmath environments you could use several & in a line for several columns or several alignment points, respectivels. In this case amsmath works also as column delimiter.

Here, you could use alignat for a numbered multiline formula with several alignments, or the block environment alignedat. Here is an example, which does the required alignment. The argument to alignedat means the number of aligned columns. Have a look at the amsmath user's guide for a complete explanation how those environment work.

    &C_1:  &x= y \implies z(t) = x(t)+ iy(t)= (1+i)t \qquad 0 \leqslant t \leqslant 1 \\
    &&f[z(t)] = Re z(t) = t, \quad dz = (1+i)dt  \\
    &&\int Re z dz  = (1+i) \int_{0}^{1} t dt = \frac{1}{2}(1+i) \\[1cm]
    &C_2:  &z(t)  =
      \left\{\!\! \begin{array}{l}
      t \qquad  0 \leqslant t \leqslant 1 \\
      1+i(t-1) \qquad a \leqslant 1 \leqslant 2
      \end{array}\right.  \\
    &&\int_{c_2} Rez dz = \int_{0}^{1} t dt  + i \int_{1}^{2}  dt = \frac{1}{2} + i

aligned equations

You could also simply use an array environment and its flexible column alignment options, since here you don't need numbering and no alignment on relation symbols.

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I used it but as your picture there is too much black space between c2 and the formula . Is there any other environment at which I van have what I want ? – Negin Feb 10 '12 at 8:04
@Negin The space is because of the right alignment. You could add further & symbols (see amsmath manual). Regarding another environment, I updated my answer. – Stefan Kottwitz Feb 10 '12 at 8:18

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