\begin{array}{r}，\begin{array}{l}，\begin{array}{c}

r：right

y = \left\{ \begin{array}{rr}
a & 12345\\
b+x & 78\\
l &910
\end{array} \right.

y = { a 12345 b + x 78 l 910 y = \left\{ \begin{array}{rr} a & 12345\\ b+x & 78\\ l &910 \end{array} \right. y=⎩⎨⎧​ab+xl​1234578910​

l：left

y = \left\{ \begin{array}{ll}  
a & 12345\\
b+x & 78\\
l &910
\end{array} \right.

y = { a 12345 b + x 78 l 910 y = \left\{ \begin{array}{ll} a & 12345\\ b+x & 78\\ l &910 \end{array} \right. y=⎩⎨⎧​ab+xl​1234578910​

c：center

y = \left\{ \begin{array}{cc}  
a & 12345\\
b+x & 78\\
l & 910
\end{array} \right.

y = { a 12345 b + x 78 l 910 y = \left\{ \begin{array}{cc} a & 12345\\ b+x & 78\\ l &910 \end{array} \right. y=⎩⎨⎧​ab+xl​1234578910​