原式=4a2-b2+3（4a2-4ab+b2）+12a2-9ab=4a2-b2+12a2-12ab+3b2+12a2-9ab=28a2-21ab+2b2，当a=-1，b=2时，原式=28-21×（-1）×2+2×4=28+42+8=78．
