In a \(\triangle ABC\), if \(r_1=12,\; r_2=18,\; r_3=36\), then \(\Delta=\)
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Remember the important identity
\[
\boxed{\Delta
=
r_1r_2r_3
\left(
\frac1{r_1}+\frac1{r_2}+\frac1{r_3}
\right)}
\]
which directly gives the area when the three exradii are known.