(1)原式=(x²+5x)²+(x²+5x)-8-4=(x²+5x)²+(x²+5x)-12=(x²+5x+4)(x²+5x-3)=(x+4)(x+1)(x²+5x-3)(2)原式=36(x+2y)³-4(x+2y)=4(x+2y)(9(x+2y)²-1)=4(x+2y)(3(x+2y)+1)(3(x+2y)-1))=4(x+2y)(3x+6y+1)(3x+6y-1)(3)原式=(x-3y)²-(x-3y)-12=(x-3y-4)(x-3y+3)