由题设得
xy=3,xz=15,yz=99-xy-xz=99-18=81
2x^2+9y^2+9z^2=(2/(yz)^2+9/(xz)^2+9/(xy)^2)*(xyz)^2
=(2/81*81+9/15*15+9/9)3*15*81=10/9+9*81/5+3645
=6611/45+3645