A cura di: Alfredo Bochicchio

$9/7x^2zxx(-4/9x^2z^3+1/3x^2z^3-5/4x^2z^3)$
$(+9/7xx-4/9)x^4z^4+(+9/7xx+1/3)x^4z^4+(9/7xx-5/4)x^4z^4$
$-4/7x^4z^4+9/21x^4z^4-45/28x^4z^4$
$(-4/7+3/7-45/28)x^4z^4$
$(-1/7-45/28)x^4z^4$
$(-4-45)/28x^4z^4$
$-49/28x^4z^4$
$-7/4x^4z^4$