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
答
①(a+3)(a-7)+25,
=a2-4a-21+25,
=a2-4a+4,
=(a-2)2;
②81a4+16b4-72a2b2,
=(9a2-4b2)2,
=(3a+2b)2(3a-2b)2.