初一简便计算 (1)51*49 (2)99²
问题描述:
初一简便计算 (1)51*49 (2)99²
答
(1)51*49
=(50+1)(50-1)
=50^2-1
=2500-1
=2499
(2)99²
=(100-1)^2
=10000-200+1
=9800+1
=9801
答
51*49
=(50+1)(50-1)
=50²-1²
=2500-1
=2499
99²
=(100-1)²
=100²-2x1x100+1²
=10000-200+1
=9800+1
=9801