①（a－b）²－1
=(a-b+1)(a-b-1)
②36x²y²－25
=(6xy+5)(6xy-5)
③49－25a²
=(7+5a)(7-5a)
④16（a－b）²－25（a＋b）²
=[4(a-b)+5(a+b)][4(a-b)-5(a+b)]
=[4a-4b+5a+5b][4a-4b-5a-5b]
=(9a+b)(-a-9b)
=-(9a+b)(a+9b)
⑤x的四次方－x²
=x²(x²-1)
=x²(x+1)(x-1)
⑥負(fù)二分之一a²＋2b²
=2b²-a²/2
=(4b²-a²)/2
=(2b+a)(2b-a)/2
⑦x的三次方－4x
=x(x²-4)
=x(x+2)(x-2)
⑧x的四次方－1
=(x²+1)(x²-1)
=(x²+1)(x+1)(x-1)
⑨負(fù)九分之一x²＋81y²
=81y²-x²/9
=(9y+x/3)(9y-x/3)
⑩（a－1）＋b²（1－a）
=(a-1)-b²(a-1)
=(a-1)(1-b²)
=(a-1)(1+b)(1-b)