1) 9(a-b)^2-12(a-b)+4
=[3(a-b)]²－2×3×2(a-b)＋2²
=[3(a-b)－2]²
=(3a－3b－2)²
2) 9-x^2+12xy-36y^2
=9－(x²－12xy＋36y²)
=3²－(x－6y)²
=(3＋x－6y)(3－x＋6y)