How is it possible to make a big right curly brace and have something like this in an equation array block?

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My code doesn't work, can anyone find the problem? The left curly brace at the end of the array is small, not big.

(\frac{1}{2} \pi_b+ \frac{1}{2}\pi_a) \pi_b+\\
\frac{1}{2} \pi_b(1-\pi_a-\pi_b) 
\end{array} \right. \left\} =\pi_b/2$
  • mathtools has an rcases env for this purpose
    – daleif
    Commented Nov 19, 2015 at 9:20
  • place \left. before the array and \right\} after it
    – cgnieder
    Commented Nov 19, 2015 at 9:21

1 Answer 1


The \left. and \right\} instructions have to be placed outside the array environment.


\left. \begin{array}{r} 
\frac{1}{2}( \pi_b+ \pi_a) \pi_b\\[1ex]
{}+\frac{1}{2} \pi_b(1-\pi_a-\pi_b)
\end{array} \right\} 


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