【3a²＋2分之1b²】[3a²－2分之1b²]【9a的4次方－四分之一b的4次方】
=(9a^4-1/4b^4)(9a^4-1/4b^4)
=(9a^4-1/4b^4)^2
=81a^8-9/2a^4b^4+1/16b^8