Question Number 141580 by learner001 last updated on 20/May/21
$${i}\:{am}\:{finding}\:{it}\:{difficult}\:{to}\:{form}\:{a}\:{pde} \\ $$$${from}\:{the}\:{function}\:{f}\left({x}+{y}+{z},\:{x}^{\mathrm{2}} +{y}^{\mathrm{2}} +{z}^{\mathrm{2}} \right). \\ $$