因式分解: ①(a+3)(a-7)+25 ②81a4+16b4-72a2b2

问题描述:

因式分解:
①(a+3)(a-7)+25
②81a4+16b4-72a2b2

①(a+3)(a-7)+25,
=a2-4a-21+25,
=a2-4a+4,
=(a-2)2
②81a4+16b4-72a2b2
=(9a2-4b22
=(3a+2b)2(3a-2b)2