先化简,再求值:y＾n(y＾n+9y-12)-3(3y＾n-1-4y＾n),其中y=-3,n=2.

y＾n(y＾n+9y-12)-3(3y＾n-1-4y＾n)
=y＾2n+9y＾(n+1)-12y＾n-9y＾(n-1)+12y＾n
=y＾2n+9y＾(n+1)-9y＾(n-1)
=(-3)^4+9*(-3)^3-9*(-3)^1
=81-243+27
=-135