(4)运用上述乘法公式计算(a+b)(a-b)=a^2-b^2 (m+n-1)(m-n+1) 999^2-1000*998
问题描述：
(4)运用上述乘法公式计算(a+b)(a-b)=a^2-b^2 (m+n-1)(m-n+1) 999^2-1000*998
答
(m+n-1)(m-n+1) 999^2-1000*998
=[(m+(n-1)]*[m-(n-1)]
=m^2-(n-1)^2
999^2-1000*998
=999^2-(999+1)*(999-1)
=999^2-(999^2-1)
=1