(1)(a+6b-4c)(a-2b+2c)
(2)原式=9x²-x²y²+y²-1+8xy
=9x²+6xy+y²-(x²y²-2xy+1)
=(3x+y)²-(xy-1)²
=(3x+y+xy-1)(3x+y-xy+1)
(3)(a-3b)(a-3ab+3b²)
(1)(a+6b-4c)(a-2b+2c)
(2)原式=9x²-x²y²+y²-1+8xy
=9x²+6xy+y²-(x²y²-2xy+1)
=(3x+y)²-(xy-1)²
=(3x+y+xy-1)(3x+y-xy+1)
(3)(a-3b)(a-3ab+3b²)