①81a^2-25b^2 ②a^2-4=(a+2)(a-2)
=(9a+5b)(9a-5b)
③-9a^2+b^2
= b^2-9a^2
=(b+3a)(b-3a)
④121a^4b^6c^2-100
=(11a²b^3c)²-10²
=(11a²b^3c+10)(11a²b^3c-10)
有什么不明白的可以继续追问,
①81a^2-25b^2 ②a^2-4=(a+2)(a-2)
=(9a+5b)(9a-5b)
③-9a^2+b^2
= b^2-9a^2
=(b+3a)(b-3a)
④121a^4b^6c^2-100
=(11a²b^3c)²-10²
=(11a²b^3c+10)(11a²b^3c-10)
有什么不明白的可以继续追问,