原式=(x²-5x+4)(x²-5x+6)-24
=(x²-5x)²+10(x²-5x)+24-24
=(x²-5x)(x²-5x+10)
=x(x-5)(x²-5x+10)
原式=2a(x-5y)-b(x-5y)
=(x-5y)(2a-b)
原式=ab(x²-y²)-xy(a²-b²)
=abx²-aby²-xya²+xyb²
=ax(bx-ay)+by(ba-ay)
=(bx-ay)(ax+by)
原式=9-(a+3b)²
=(3+a+3b)(3-a-3b)
原式=(a²-2ay+y²)-(b²-2bx+x²)
=(a-y)²-(b-x)²
=(a-y+b-x)(a-y-b+x).