Х³-у³ х²-ху+у²
----------------- * -------------------- =
х³+у³ х-у
(х-у)(х²+ху+у²) х²-ху+у² (х²+ху+у²) (х²+у²) +ху
= ------------------------ * ------------------- = ---------------------- = ---------------------- =
(х+у)(х²-ху+у²) х-у (х+у) (х+у)
(х²+у²) +ху (х+у)²-2ху+2ху
= ----------------------- = -------------------------- = (х+у)
(х+у) (х+у)