  An integral operator $M$ is constructed performing a separation of variables
for the 3-particle quantum Calogero-Sutherland (CS) model. Under the action of
$M$ the CS eigenfunctions (Jack polynomials for the root system $A_2$) are
transformed to the factorized form $\phi(y_1)\phi(y_2)$, where $\phi(y)$ is a
trigonometric polynomial of one variable expressed in terms of the ${}_3F_2$
hypergeometric series. The inversion of $M$ produces a new integral
representation for the $A_2$ Jack polynomials.
