用简便方法计算3道
问题描述:
用简便方法计算3道
(1) 53²-47²
(2)14*2/3×15*1/3
(3) (1-1/2²)·(1-1/3²)·(1-1/4²).(1-1/10²)
答
(1)原式=(50+47)(50-47)
=600
(2)原式=14×(15×2/3×1/3)
=140 /3
(3)原式=(1-1/2)(1+1/2)(1-1/3)(1+1/3)·····(1-1/10)(1+1/10)
=1/2×3/2×2/3×4/3···9/10×11/10
=11/20