# Align equation multiple columns

Is it possible to align an equation like this:

I tried this, but:

\begin{align*}
& u_a(t) &= u_e(t) - u_{R1}(t) \\
&        &= u_e(t) - R_1 \cdot i_1(t) = u_e(t) - R_1(i_2(t) + i_3(t)) \\
&        &= u_e(t) - R_1 \cdot i_2(t) - R_1 \cdot i_3(t) \\
&        &= u_e(t) - R_1 \cdot \frac{u_a(t)}{R_2} - R_1 \cdot C \cdot \ddt[t]{u_a(t)}\\
<=> & u_a(t) + u_a(t) \cdot \frac{R_1}{R_2} + C \cdot R_1 \ddt[t]{u_a(t)} = u_e(t) \\
\end{align*}


• And what is the \dd macro, please? – Bernard Oct 7 '14 at 20:28
• That's just for the derivation fraction df(x)/dx – dersimn Oct 8 '14 at 8:21

For multiple alignments you can use aligned inside align.

\begin{align*}
& \begin{aligned}
u_a(t) &= u_e(t) - u_{R1}(t) \\
&= u_e(t) - R_1 \cdot i_1(t) = u_e(t) - R_1(i_2(t) + i_3(t)) \\
&= u_e(t) - R_1 \cdot i_2(t) - R_1 \cdot i_3(t) \\
&= u_e(t) - R_1 \cdot \frac{u_a(t)}{R_2} - R_1 \cdot C \cdot
ddt[t]{u_a(t)}\\
\end{aligned}\\
<=> & u_a(t) + u_a(t) \cdot \frac{R_1}{R_2} + C \cdot R_1 ddt[t]{u_a(t)} = u_e(t) \\
\end{align*}