Question

4(a-b)²-16(a＋b)² m²n²-1／4（m²＋n²）² 这两道题怎么做？

急急急~多谢帮助

Answer 1

因式分解吗？如果是：
原式=[2(a-b)]² - [4(a+b)]²
=[2(a-b)+4(a+b)][2(a-b)-4(a+b)]
=(2a-2b+4a+4b)(2a-2b-4a-4b)
=(6a+2b)(-2a-6b)
=2(3a+b)•[-2(a+3b)]
=-4(3a+b)(a+3b)
原式=(mn)² - [(1/2)(m²+n²)]²
=[mn + (1/2)(m²+n²)][mn - (1/2)(m²+n²)]
=(1/2)[2mn+(m²+n²)]•(1/2)[2mn - (m²+n²)]
=(1/4)(m+n)²•[-(m-n)²]
=(-1/4)(m+n)²(m-n)²